Takes place around 'The Last Man part 1', the final episode in season four.

Tomorrow's gone

"Go and see him, Radek. Please. Maybe you can talk some sense into him."

"I am not sure what I can say. You are his sister, would it not be better if..."

"He won't listen to me, Radek. He probably won't listen to you either. But I just – I want someone to speak to him. Someone he trusts."

"He trusts you."

"No. He loves me. But he doesn't trust me." The image of Jeannie flickers. Radek pretends he cannot see the sadness in her expression. "I'm not expecting miracles, Radek. And I know it's a lot to ask. But something needs to be done and I – I can't."

He sighs. "No miracles. But I will try."

*

Radek walks past students, following the signs through the university campus towards the central library and the coffee shop within. He tries not to remember his own university days – to think of how old that makes him feel – and instead concentrates on appreciating the architecture. Modern, gleaming, but still a place of learning in the traditional sense. Green spaces divide the buildings, and young trees provide shade for students. Several banners hang from windows, protesting about the latest cause.

No one looks at Radek. He isn't sure if they assume him to be a parent, a lecturer, or a caretaker.

He smooths a hand over his scalp self-consciously, tugs at his jacket, and ignores the twinge in his knees as he climbs the steps to the library entrance. At reception he signs in, then passes through security, showing the guard the limited contents of his bag. He packed lightly, not intending to stay for long. His wife waits for him at home, and his new granddaughter.

The coffee shop is at the back of the library. Radek walks down the central aisle, comforted by the familiarity of bookshelves and their contents. The building is several stories tall, and a glass roof allows light to flood through a filter designed to protect the paper and ink below. The floor is tiled, and the high heels of the girl in front of him bounce echoes into the ceiling.

It isn't difficult to find the coffee shop, but locating a spare table proves harder. Eventually he finds a small booth in the corner and negotiates his way to it, catching the eye of a waitress. Five minutes later and he is enjoying a strong coffee and a slice of thick, dark chocolate cake – recommended by neither his doctor nor his wife.

Twenty minutes later and he has finished the cake, sipping the coffee slowly and reading a paper he brought with him.

Fifty minutes later and the cake is only a memory. He orders a second coffee, and is close to seeing the bottom when McKay finally appears.

He saw Rodney only a few months previously via the 'net, but the image on a video call hides the finer details. McKay is a little rounder and a little heavier than Zelenka remembers, hair thinning and grey, eyes dimmed and skin lined. He is wearing an ugly cardigan, stained on the left shoulder. He takes the seat opposite Radek, snaps his fingers at the waitress, and despite the superficial changes in that moment of irritation he looks exactly like his younger self.

"You've already ordered?" McKay sounds surprised.

"I have been here some time, Rodney," Radek reprimands.

"I'm not that late."

"Over an hour. And I came from Europe, and you from across the street."

"I took a taxi," McKay says, petulantly.

Radek chooses not to pursue the argument. "How are you?"

"Fine. Good. You?"

"I am well."

"Any papers published recently that I might have missed?"

"Not at the moment," Radek replies. "You?"

McKay shrugs. "I'm too busy."

"Really? Doing what?"

"The usual."

Radek raises an eyebrow. "The usual?"

He receives a dark look in return for his probing. "You know what. It's the only thing that matters."

"Not the only thing, Rodney." He is prevented from saying more by the arrival of the waitress, bearing two cups of coffee and another slice of the chocolate cake.

McKay takes the cake and one of the cups, then pushes the other over to Zelenka. "Consider it an apology for arriving late."

"Apology accepted." Radek takes a sip of the coffee, hot and bitter against his tongue.

"What are you doing here, anyway?" McKay asks, around a mouthful of cake. "Have I missed a birthday?"

Radek has prepared himself with a lie. "With the baby, and all the fussing Janica does, I decided to take a trip away, to leave them to themselves for the day. And I thought, why not see you?"

"It's been a while."

"So," he takes a breath, feeling nervous, "how does it go?"

"I'm close." Rodney digs into the cake with his fork, furiously. "I know it. Just a few pieces need to slot into place." He glances at Radek. "You could help?"

The offer cannot remain unrecognised. "You are asking for my help, Rodney? How many years have we known each other, and this is the only the third or fourth time?"

Rodney scowls. "Look, you know what I think about your work. You don't need me to say that I..."

"Respect me?" Radek finishes, restraining a smile.

"It would go quicker with some assistance."

"Sadly, I cannot. I have family commitments. But perhaps you could ask one of your students?"

McKay snorts disgustedly. "They're all idiots. I swear, I think they're being bred more stupid. One or two out of a class of forty might make some success out of their lives, but the rest will end up being doctors or dentists or something else equally useless."

This Radek allows to pass without comment. He is used to the ranting. And Radek is hesitant, bracing himself before uttering his next words. "What about Jeannie?"

McKay's face turns thunderous. "Jeannie thinks I'm obsessed."

"Well..." Radek chooses his words carefully, "you have been very focused, these past years Rodney. You have been working on this project ever since..." He hesitates, briefly. "Since as long as I can remember."

McKay leans forward, allowing the background noise of the coffee shop to dim his words. "It's the most important project I've ever worked on. The most important project there is. You know that."

"That is what you have said, all this time."

He winces beneath McKay's glare. "You know the effect it could have. You know what I'm trying to stop."

"But after so long without success, do you not think that perhaps it is time to..."

"To give up?"

"No," Radek says, quickly. "But perhaps you might find other priorities."

Rodney looks away. "It's too late for that," he says, the words coming out in a rush, as though the truth is too hard to voice. "Besides, when this works..."

"If..." Radek corrects.

He is ignored. "When it works, then it will be like a do-over. Better. They'll all be alive." McKay's eyes brighten. Radek realises that it is only when talking about the past that Rodney becomes animated.

It was not always like this. He has to remind himself of that. There have been Christmases, birthdays, holidays. Events at which Rodney has connected with the outside world, for a little while.

Radek reaches into his pocket and pulls out his wallet. Hidden behind his identity card there is a photo, neatly folded. He pulls it out and pushes it across the table towards Rodney.

"This is Kalena."

Rodney picks up the photograph. "Who?"

"Kalena, Rodney. Her mother is Janica. My eldest daughter. Your god-daughter. I sent you an email telling you all of this. You knew Janica was pregnant. You sent a card."

"Oh." Rodney blinks. "Of course. I knew that. I just..." He flounders. "Nine months? It's been that long?"

"Closer to ten, actually."

The Canadian reconsiders the photograph. "She's, ah... she looks healthy." He passes the photo back awkwardly. "I'll send something."

Radek picks up the photograph and looks at it. He may be biased, but he thinks Kalena is beautiful. The pregnancy was difficult, the birth dangerous, but both mother and daughter are now recovered. He is reminded for a moment of the terrible, crippling fear experienced when he thought he might lose them both. Janica's husband forced out of the room to make room for doctors and nurses and equipment, his face white, entire body shaking. Radek holding his wife's hand tightly, listening to her whispered prayers and wishing he believed in a god he could appeal to.

The existence of his granddaughter is a miracle he can believe in.

"So, I guess this makes you a grandfather, huh? Congratulations, Radek."

The memory abruptly ends, and Radek is almost overwhelmed by a rush of anger. He snaps, not thinking before he speaks: "Congratulations, Rodney? You would congratulate me?"

McKay moves back a fraction, clearly bemused. "Well, yes. Being a grandfather is a good thing, isn't it? And hey, since I'm Janica's godfather does this make me some sort of grand-godfather?"

"Why?" Radek bites back. "Does it matter? Do you care about them?"

McKay's eyes widen. "What? Of course I care! Look, if this is about forgetting a birthday card or something..."

"No." He takes a deep breath, trying to control his feelings. "This is not about that." He folds the photograph carefully, fingers trembling, and puts it back into his wallet. "I am sorry, Rodney. I should not – for a moment, I forgot myself. I am angry about something else, and I was taking that out on you."

Rodney shakes his head. "No," he challenges. "I don't think so. I've had enough people shout back at me to know when I'm the one they're angry at. And I know when you're doing it. So what, Radek? Is this because I didn't read your email, because I didn't know Janica had given birth?"

Radek stares at his hands. The noise of the coffee shop around them seems suddenly oppressive, as though the life contained in the chatter of voices and clatter of the coffee machine is mocking them both. "Do you know why I made you godfather to Janica, Rodney?"

The physicist shrugs. "It's what you do, isn't it? One of those outdated traditions."

"But why you?"

"I don't know. I suppose, if anything had happened, you would want her to get a good education."

"There was that, yes. But I also believed you would care for her, Rodney. You have your flaws, but I have seen you with Jeannie, and with your niece, and I saw you on Atlantis." He drops his voice a little, conscious of the crowd around them. "I saw you change."

McKay flushes, looking away. "That seems like a lousy reason..."

Radek interrupts. "Anica did not agree with me. She thought I was mad, suggesting that you be the one to take care of our daughter if something happened to us. But I convinced her, eventually. I knew that you would take time to adjust, but that you would come to care for our daughter as much as a father would, that you would protect her and love her because you are a good man."

Rodney coughs, clearly embarrassed. "Radek..."

"But now, as we sit here, I realize you do not care for her at all. She does not matter to you. None of us matter to you." He feels his anger rise once again, but this time does not make any effort to control it. The memory of his fear is too fresh, his emotions too raw. It is too late, of course, but Radek realises now that he was the wrong person for Jeannie to choose.

"I don't think a couple of forgotten birthdays mean that I..."

"Tell me, Rodney – if something happened now, if something terrible happened and the only one left to care for Kalena was you – would you? Would you look after her, as you promised to look after Janica when she was born?"

"That's not a far question to ask!" McKay shoots back. "Things are different now. I'm older. And I have priorities..."

"A wife, children of your own? No, you mean this project of yours, this great dream you have. You would turn my granddaughter away because you would rather pursue ghosts. But they are dead, Rodney. Kalena is not."

He stops, breathless, heart pounding beneath his ribs. He did not come here intending to argue, but had he thought before, Radek should have known this would happen.

Across the table, McKay presses his lips into a thin line and for a long time says nothing.

Radek puts both hands around the coffee mug and presses down hard on the ceramic. Again the noise of the coffee shop threatens to overwhelm him.

"This isn't just about them." McKay speaks quietly. He sounds tired, as though he has conducted this argument a thousand times.

Perhaps he has, Radek thinks, remembering his conversation with Jeannie.

"This time-line isn't supposed to exist. It's wrong. Too many people were lost, Radek. Not just," Rodney's voice breaks by a tiny fraction, "not just Sheppard and the others. But everyone in the Pegasus galaxy, everyone Michael's army attacked."

He speaks in a whisper, but in this busy environment no one is paying two old men any attention.

Radek relaxes his hold on the coffee mug. He suddenly feels as tired as Rodney sounds, weighed down by the knowledge that his words will not help, that he is speaking to someone already lost. "You can lie to me, Rodney, but do not lie to yourself. You are not doing this for Michael's victims."

"Radek, thousands died. Thousands are still dying for all we know..."

"And perhaps knowing that, telling yourself what you are doing is for them – perhaps in that way you can justify your actions. But you are in denial." He looks up from the coffee mug and meets his friend's gaze. "Tell me the truth, Rodney. If Sheppard had returned, if Ronon, Teyla and Carter were still alive, if Jennifer had survived – would you still work on a way of undoing history?"

"If that had happened then Michael wouldn't have won."

"You don't know that. It is entirely possible that Michael would have succeeded even with the others fighting against him." Radek pauses, hating himself a little. "Now answer me, Rodney – if Jennifer had survived, would you still be doing this?"

He can barely remember Doctor Keller's face or voice. Memory is distorted by the intervening years. For Rodney, history clearly feels more recent.

"I don't know," McKay snaps back, his face pale. "She died. Slowly. In pain. I couldn't stop that. I couldn't stop any of it. Teyla, or Ronon, or Carter. But I can do something. I can. If I bring Sheppard back..."

"Then you hope you will bring them back. Undo your loss. Because this is about you, Rodney. Not Pegasus, not Michael. You." Radek leans forward, aware of how harsh his voice sounds. "We all experienced loss, Rodney. You were not the only one grieving."

"But I'm the only one who can do something about it." Rodney's voice is defiant.

"No. You are the only one who chose not to move on. The rest of us did. We continued living. We found new jobs, and partners, and families. Miko Kusanagi is a well respected professor living in Tokyo. She has eight children. Did you know that? Doctor Kenworth is a world renowned expert on defensive weaponry. He was nominated for the Nobel Prize two years ago. What about Libby? Jeannie told me she was in her final year at Harvard, and doing incredibly well. Her sister, Madeleine – she is pregnant. Three months, I believe. Jeannie will be a grandmother and you will be a great-uncle."

"I know," McKay retorts. "I know all of this, but..."

"But what? But their lives do not matter?" The volume of Radek's voice rises. "Their existence?"

"Of course they matter..."

"You are lying! If they mattered at all to you then you would make different choices. You would leave the past alone."

"This time-line is wrong," Rodney insists, but there is a desperation to his voice, a high-pitched quality which threatens hysteria. "This universe shouldn't exist!"

Radek shakes his head, reliving the pain he felt at the realisation that he might lose Janica, that he might lose both his daughter and the child she carried within her. "But it does! My family and yours, they exist, yet you are obsessed by the idea of undoing all of that!"

"There's nothing to say that when my plan works, they won't still exist in the other time-line!"

"You know that isn't true."

McKay shakes his head. "Things will be better..."

"For you, perhaps. But not for the rest of us. I would rather choose my family, and this life, over any you would try and create." Radek pushes the coffee mug away and gets to his feet. "I am sorry for coming here. Jeannie thought I could speak rationally to you. I see now she was naïve."

"Hah. Then Jeannie did send you. I thought so."

"Rodney..." Radek turns away, his right hand curled into a fist.

Rodney watches him gather his belongings, jaw clenched, chin lifted in defiance. Finally, just as Radek pushes his way out of the booth, Rodney speaks.

"I didn't think you were so selfish, Radek. Or so stupid."

Radek feels the shape of his wallet press against his chest, nestled within an inner pocket of his jacket. "You keep telling me that this time-line is wrong. I disagree. This time-line is the one that simply is, Rodney. You are the one who does not fit in it."

Then he leaves, believing this is the last time he will speak to Rodney McKay.

He is wrong.

*

The last time Radek Zelenka sees Rodney McKay is a Thursday.

Four months have passed since the incident in the coffee shop. Radek has done his best not to think of it, and for the most part, succeeded. He divides his time between work and his family, spending all the time he can with his daughter and granddaughter, or as much as his wife will let him.

Radek had stopped believing in love several years before meeting Anica. He had not thought it possible to love someone so much, to feel that ache in the pit of his chest when he thought of losing them, that even the imagined loss would cause him pain. Then Anica gave birth to their daughter, and though Radek had not thought it possible, his feelings only grew stronger. He loved every day with his small family, and suddenly work, the pursuit of science, did not seem as important as it once had. With the addition of Janica's husband and their daughter, Radek wonders if his life has become perfect. He relishes the part of grandfather, and looks forward to reliving the days of building snowmen, trips to playgrounds, and having a small hand clasped in his when walking down the street.

He does not think of Rodney very much, and when he does it is mostly with anger. Anger and then sadness, as he thinks of all that has been lost, and all that Rodney has missed out on.

He does not expect to hear from Rodney again, thinking that their last argument had left every bridge burnt. Rodney is the one to extend the invite, so Radek knows the situation is urgent. The Canadian leaves a video message, and on it he seems excited; eyes bright, body bouncing on his heels, speed fast and babbled. Just like old times.

Rodney does not mention the argument. Nor does he state the reason for his call; only that he can't explain over video, and he needs to see Radek to explain. Face to face.

Radek sits in silence for a while after playing the message, considering the request. Eventually Anica comes into the room, concerned.

"What is it?"

He thinks of Atlantis, and missed opportunities, and the possibility that a man might change, even at his age.

"I need to go to Canada."

She responds by shaking her head, and says: "Nothing will have changed."

Radek thinks she is probably right. Nevertheless, he entertains himself with the idea that Rodney has found a new project, some new discovery. That the result of their argument was not alienation, but a moment of clarity. Perhaps he has made progress at the university, or perhaps he has been called upon by the government, or by Stargate Command. Even now, so many years later, both he and Rodney could be called on to act as consultants. Rodney always refused. But Radek hopes that this time is different.

Perhaps, Radek wonders, perhaps Rodney has met someone.

He entertains this delusion until he arrives in Canada, skin still prickling from the transporter technology. Then the alien nature of his surroundings bring him back to reality. He is delayed at security while his bag is searched; he struggles over his English when asking at the desk for directions; he gets a scowl from the taxi driver when he pays with a large denomination note.

The taxi drops him outside Rodney's apartment building. He lingers on the front step while waiting for Rodney to buzz him in, trying to guess what their meeting will be like.

Rodney opens the apartment door so soon after his knock that Radek suspects he has been waiting behind it. The Canadian greets him with a hug; awkward but not unwelcome. Radek pats his shoulder, twice, then pulls away.

"It is good to see you again."

"Come in." McKay gestures at the room. "Make yourself at home."

Radek follows him inside, shutting the door behind him. "I am surprised you called," he admits, waiting in the middle of the room while Rodney busies himself in the kitchen. "I did not like the way our last conversation ended."

"Oh, that." Rodney's tone is dismissive. "A difference of opinion."

"A little more than that," Radek says, reproachfully. But he says the words quietly. He did not come here to have another argument.

The apartment is tidier than Radek remembers. Surfaces are clean and, for the most part, free of debris. The furniture is not obstructed by lab equipment. The floor is free of papers and wires. Even Rodney himself seems in order, clothes clean and hair smoothed down. The only exception to the sanity of the room are the four large whiteboards, wedged in between the couch and the wall, but even they seem neater, the handwriting less of a scrawl.

Rodney emerges from the kitchen with two bottles of beer. He passes one to Radek, then takes a gulp from the other.

When Radek stops to think, he realises he is not sure why he came. His previous fantasy has long since dissipated. Perhaps he hoped for reconciliation. But no – it was more than a difference of opinion that drove Radek home the last time.

He had apologised to Jeannie. Said the words, "he is too far gone."

"So, how are you?" Rodney sounds breathless, seeming to struggle to contain his excitement.

"Good."

"And the family?"

"Very well. Anica sends her love. Janica thanks you for the bundle of baby clothes you sent. Kalena is doing well, she is putting on weight, and is able to interact with us..."

Radek's voice trails off as he realises that Rodney is not listening, that the question was asked from a sense of obligation, than genuine curiosity or concern. It is then that he asks himself why he did not listen to his wife, why he travelled across the world despite her warnings. He realises that he came to hear Rodney's next words. Words that have always been inevitable, no matter how many times Radek insisted it could not be done.

"I did it," Rodney says triumphantly. He has rearranged the boards, and taps the nearest. "I did it, Radek!"

Radek stares at him, the words slow to register.

"See?" Rodney asks, pointing at the writing on the board. His finger follows the lines of text, the equations and notations.

Radek reads over the script, trying to understand McKay's handwriting. His stomach churns, acid burning at the back of his throat.

"I mean, it wasn't easy... well, parts of it were easy... but the rest, well... I had to bend a couple of laws of physics – hell, more than a couple, but that's never been a problem before – and now I've done it I wonder if there wasn't a quicker way, but still, you can't deny the fact that it's all there, that the calculations are right... I'm mean of course they're right, but I still triple checked them, just in case..."

Radek barely hears Rodney's babble. He concentrates on the whiteboards, only comprehending a fraction of his friend's work, but grasping with a sense of horror what McKay claims to have done.

"You located Sheppard?"

"That was the easy part."

"You found a way to bring him back?"

"Not bring him back, send him home," Rodney corrects.

"To Earth?"

"Of course not to Earth, that would be impossible... well, not impossible, but extremely improbably... no, I'll send him back to Atlantis. Our Atlantis. At the time he left."

"But it is impossible," Radek protests. He feels ill. "Jeannie and I both worked on this. There is no way..."

"You gave up too soon." There is no bitterness or recrimination in McKay's voice. "The answer was there – it just needed looking at from a different direction. We spent so long trying to bring Sheppard back here, when what we needed to do was send him back home. Travelling in time, not space." Then he pauses, bouncing on his heels, looking just as excited as he had in the video message.

Slowly, Radek pulls out the white boards one by one and tries to make sense of Rodney's work. He has only limited success. The formulas on the boards are multi-layered and deeply complex. There are leaps of logic that seem unconnected to context. The work references theories that are unknown to him. In a strange moment of deja-vu Radek is reminded of Rodney's work when he was trying to ascend. Then, as now, he could only understand snatches, the occasional word or phrase, but the rest was incomprehensible. And then, as now, the writing was tinged with mania.

One thing he is certain of, even if he cannot understand the work. Rodney is telling the truth.

The shock is overwhelming. He staggers backwards, bumping into the couch, the beer bottle almost slipping from his fingers.

"When were you at Atlantis?" he demands. "You needed to program the system there, yes?"

"Yes, and not yet." McKay scowls. "The only one I still know there is Lorne, and he's in Russia until tomorrow. I left a message with some of his subordinates – fortunately, my name still holds a small amount of leverage in the right places. But," he brightens, "I don't suppose it matters when I leave the message. This time line is irrelevant now."

The offhand way he describes what he has done angers Radek. "Irrelevant, Rodney?"

McKay seems not to hear him. He turns his back on Radek and begins to pull out a second whiteboard. "See, I thought at first that the problem was in triggering a wormhole that returned Sheppard to the moment he left, but then I realised that the power level would be the hard part – and programming in the coordinates so the wormhole looped back on itself. However, after the black hole incident Carter had done some work which proved useful..."

There is a roaring in Zelenka's ears, drowning out Rodney's words. He feels faint.

It is possible that Rodney is wrong. After all this time, perhaps his obsession has led to mistakes. Perhaps, Radek wonders, Rodney's plan is nothing more than a dream.

No. It is a long time since Atlantis, but Radek spent enough time working below Rodney to recognise when the Canadian has achieved real success. He is not infallible, is not beyond making mistakes – even aboard Atlantis – but not in this case.

He has always known it was possible. But a theory is a long way from fact.

The theory is sound...

"But if you do this," Radek says, his voice sounding trapped and tight, "if you send Sheppard back, then you risk changing the time-line."

"That's the general idea." Rodney smiles, and the image is frightening. "I'll be able to undo everything. If Sheppard goes back, then he can save Teyla, and none of this needs to happen. Ronon, Carter, Jennifer – they don't need to die."

"But they did die, Rodney." His voice is trembling now, and he hates it. "They died many years ago. The rest of us, we survived. The world changed and we have lived through it."

"But it doesn't have to be like this. Not now."

Radek raises his head and meets his friend's gaze. He realises from the look in Rodney's eyes that his words will have no effect, but he speaks anyway. "Rodney, please. Do not do this. You have spent enough of your life on this. Let go."

"Let go?" McKay's gaze hardens, and he scowls. "Nothing has changed, has it? Even now you're here, with the proof in front of you? I thought that if you were here you'd be able to see it but you can't, can you? You still can't see how important this is?"

"Important to you, perhaps..."

"To the entire galaxy! To the Pegasus galaxy! Everything that went wrong, everything that was destroyed, everyone who died... I can undo all of that!"

Radek shudders. He looks back at the whiteboards, hoping for a flaw, hoping to spot something which will disprove all of McKay's claims.

"Sheppard goes back, saves Teyla, saves the baby, stops Michael. None of this has to happen. Things can be different."

Again Radek has stopped listening. He stares at the whiteboards, and as he does so a small voice in the back of his head raises a question. He looks up at Rodney, licks his lips, then says: "What about the time-line?"

Rodney breaks off in mid-rant, and stares at Radek. "What?"

"I accept that you found a way to send Sheppard back into the past, to the place and moment he left. If Lorne allows you access, you will be able to program this into Atlantis' systems. But how will you know to which time-line Sheppard will arrive?"

A frown creases McKay's forehead. His hands clench around the beer bottle. "What are you talking about?"

Radek takes a seat on the nearest couch. He leans forward, resting his elbows on his knees. His voice still trembles, as though he is a first year student again, arguing with a senior professor, but he ignores it. "There are two main theories about time travel, yes, Rodney? More, I realise, but let us begin with two."

McKay rolls his eyes. "If you're going to mention the grandfather paradox..."

"That is where this begins, yes? Two possibilities. One, that Sheppard returns to his own time at the moment he left, and in doing so is able to prevent what happened later. In stopping Michael and saving Teyla, he changes history. Our existence, this life, never exists."

"I know your feelings on that," McKay says, his voice hard.

Radek has to bite his tongue to stop himself from snapping. "Yes," he says, keeping his voice tightly controlled. "I do not mean that."

"Then what?"

"There is the second theory. The theory which states that time travel, of the manner I have just described, is impossible. It would create a paradox. Sheppard succeeds in changing history because of your actions, but if history changes then you would not exist to send him back."

McKay perches on an arm of the opposite couch, scowling. "This is grade school stuff, Radek. Has retirement addled your brain that much?"

"The second theory," Radek continues, as though McKay never spoke, "proposes the existence of a parallel universe, created at the moment Sheppard returns to, the moment he left. Our universe and it are identical to that point. Sheppard does not travel in time within his own universe, but the act of travelling causes our universe to split from the alternate. In one, Sheppard never returns and life unfolds as we have experienced it. In the other, Sheppard reappears and Teyla is rescued."

Two bright pink spots appear on Rodney's cheeks. A muscle throbs in his cheek. "So what you're saying is that you agree that my work is correct, but my view of time travel is wrong?"

"I am just suggesting that you should be prepared for nothing to change..."

"Because you think I'll send Sheppard into a parallel universe?"

"Where events will be different," Radek says. "Perhaps one in which Michael is stopped from taking over Pegasus."

"While this time-line remains in existence?"

"You found a way to send Sheppard back," Radek persists. "Surely that should be enough to change the time-line?"

Rodney stares at him for a moment, then turns his head, getting to his feet. He starts to pace, beer bottle swinging between his fingers. "It needs to be programmed into Atlantis' systems."

"And then this universe will cease to exist?"

"Yes," McKay snaps, then, "No, it will get better. It will be different."

His hesitancy is fleeting. Radek hears a note of mania in Rodney's determination, and it frightens him.

For the first time he wonders if perhaps the worst thing for Rodney is to succeed.

"SG-1 changed the time-line a number of times," McKay persists. His feet are heavy against the floorboards. He rakes his free hand across his scalp, the other tightening its grip around the beer bottle. "And my work clearly shows that it is possible. I can prove it."

"No, Rodney," Radek says, quietly.

McKay suddenly reaches out and grabs Radek's shoulder. "I want to create a contingency plan, just in case something goes wrong at the other end of time. Help me with it."

"Rodney..."

"Don't think I haven't thought of the risks. I have to assume that Atlantis will still be in existence when Sheppard arrives, that it won't have been destroyed by the Wraith or some other entity. The computer systems may no longer work. There might not be enough power for the Stargate to operate."

"There are many what ifs, Rodney," Radek says. He wonders at this strange paradox. It is the emotion of hope that has sustained Rodney for all these years, caused him to abandon the world outside for the chance of resurrecting the past. Yet now, on the cusp of success, his friend seems without that same hope, without that faith.

"It's simply cause and effect. I've already worked on the formula. If I start from the condition of Atlantis when we left and use what facts we know about the Pegasus galaxy since then..."

"Rodney..." Radek tries to interrupt.

"It could be like the old days. Working in a crisis? Well, I'll still take the lead, obviously, but it would be good to have a second mind."

"No, Rodney."

"We will need to find another way to get it to Atlantis, obviously – Lorne will start to ask questions if we go back a second time – but I'm sure there's a way around that..."

"No," Radek interrupts. "You are wrong, Rodney."

There was a time when he felt frightened by Rodney's genius. Brief moments, when danger threatened and all eyes were turned towards McKay to come up with a solution. It was then, and only then when Radek realised how glad he was that he had not won McKay's position, how he did not bear the title and the salary and the responsibility of department chief. Then, when he realised how science could make man look into the mirror, and mistake himself for a god.

This feels the same. Awe and horror mixed up together. Radek, able to understand the science but not the mind that discovered it. Not the thought processes, moving in leaps and bounds towards an incredible conclusion. One which might save lives, or might destroy a solar system.

Or an entire existence.

McKay is staring at him, mouth slightly agape, eyes hard.

For a moment, Radek is overcome by a swell of grief and pain, a reminder of all that has been lost. He can see, clearly, what drove his friend to this place. He tries to use reason as a lifeline, hoping that his denouncement can bring Rodney back from the brink.

"You are wrong."

He has little hope.

"Wrong?" Rodney says, incredulously.

Radek struggles to make his voice heard. "Your plan rests on an assumption I believe to be false."

"What?" his friend demands. "What assumption? This is all logic!"

"You are not listening to me, Rodney. There is nothing to show which theory of time is correct. Yes, SG-1 appear to have changed the past, but we only know this from their mission reports. There is no objective standard to which the continuity of time can be measured. The only evidence of time travel is the word of the traveller."

"So this is meaningless?" Rodney gestures at the whiteboards. "Radek, you can see my work! If you don't understand..."

"I understand." Radek keeps his tone low and quiet. "You have found a way to help Colonel Sheppard. That is admirable, Rodney. And I hope you are able to bring him back, I do. But I do not share your goal of using Sheppard's return to change time, nor do I believe it is possible. I cannot."

"You don't know..." McKay tries.

"I know enough. I know that I choose this world above others. And I fear for you, Rodney. I wish you would at least consider the possibility that nothing will change."

He stares at Rodney, helplessly, hoping his words have been enough. His friend turns away, shoulders tightening.

"I know I'm right," Rodney snaps. "And besides, what makes you think that your theory is any more likely? Parallel universes?"

"Faith," Radek answers, simply. His voice is strong, swelled with confidence and certainty. "Faith in this universe, Rodney. In all I have in this universe, and in all I have experienced. You cannot wipe this out."

McKay's eyes narrow. He repeats, savagely, "I know I'm right."

"Then we have nothing else to talk about." Radek gets up from his seat, and begins to walk toward the door.

"You're wrong, Radek." Rodney's words sound like a warning. "I thought you were smart enough to see the truth, I thought we could work together on this. I thought you would share my goal. If we do this, if we save Pegasus..."

Radek thinks of his baby granddaughter, her tiny hand making a fist around his finger, holding on tight.

"You are not doing this for Pegasus, Rodney." He starts to walk away from his friend, towards the door. "And I will not help."

"Then damn you." McKay's voice trembles, his fury dark and deep. "I can do this alone. I'll change the past."

More words will not make a difference. Radek opens the door to Rodney's apartment, and walks out into the corridor. Rodney stands in the room behind him, and makes no move to follow.

"You'll see, Radek."

Radek turns, and looks back at the man he no longer recognises as his friend.

"I am sorry, Rodney," he says, sincerely.

They are the last words he will ever say to McKay.

*

Life for Radek Zelenka continues.

He does not receive another message from Rodney after their last, heated argument. Returning home, Radek recounts little of what had occurred to his wife, and she does not press him for details.

He returns to the office, although these days his work is slowing, and Radek takes on shorter consultancy projects, preferring to spend time with his family. He is at home when he finds out, having spent the day babysitting his granddaughter.

"She smiled at me."

"I don't think so, father."

"She did. She recognises me."

"She sleeps and eats, that is all. She is too young."

Radek tickles his baby granddaughter under her chin. "Her development is quick, just like her mother."

"And like her grandfather." Janica smiles, clearly indulging the older man.

"Radek?"

Anica is standing in the doorway to the kitchen. Her expression is one Radek has only seen a handful of times; when her father died, when a pregnant Janica was rushed into hospital.

"There is a message."

Radek looks from her to Janica. He manoeuvres the baby into her arms, then rises from his seat.

"What is it?" Janica asks, eyes wide.

"Nothing," Anica says, "just one of your father's colleagues." She isn't convincing.

Radek follows his wife into the study. She goes to the computer, her hands moving across the screen. "It is Jeannie McKay. She must have left the message while we were out." Anica glances at him. "I think perhaps you should listen to this alone."

He stares at her, a prickling sensation running down his back. "It is bad."

It isn't a question. "I am sorry, Radek."

He reaches out and takes her hand. "Don't leave."

She pauses for a moment, then nods, and moves to stand behind him. Radek takes a seat behind the desk, then reaches out and presses the computer screen.

There is no visual to the message. His surprise ends when Jeannie starts to speak. Her voice is hesitant, breaking over the words.

"Radek. I... I wanted to tell you in person, but I couldn't... I couldn't get away. So much needs doing."

Anica's hand rests gently on Radek's shoulder. She has already heard the message once.

"I'm sorry. I'm not... it's too hard." Jeannie takes a deep breath. Radek realises she is crying. "Meredith. It's Meredith."

She doesn't say the words. She doesn't need to.

Anica's hand squeezes Radek's shoulder. He is desperately glad of her presence.

"One of his neighbours heard an explosion from his apartment. He went to the door and saw smoke, so he called the fire department. But it..." Another pause, another break in her voice. "They said it was instant. The electrics, something shorted, and Mer... Radek, I'm so sorry."

Radek reaches out and pauses the recording. He struggles to feel anything. Searches for a reaction inside himself without success. He is simply numb.

"I am so sorry."

Anica did not like Rodney. She did not understand Radek's loyalty to him, not after he had failed to live up to the trust placed in him as godfather.

The grief in her voice is real, nevertheless.

Radek presses play.

"The police..." Jeannie laughs. The sound is strangled. "The police asked how Rodney had been. As though he killed himself, Radek. I know my brother better than that. But they thought he was mad. I can understand why." Again Jeannie pauses to take a breath, and this time when she speaks, her voice shakes. "He was building a machine. An experiment. I looked over his notes, Radek. It was... it was a time machine."

There is a sudden pain in Radek's chest, a heaviness to his lungs that makes it difficult to breathe.

"God, Radek, after all of this, Mer still couldn't let it go. I should have stopped him, I should have done something. But it killed him. This obsession of his. I can't..."

There is sound on the recording, then a second voice speaks. Caleb. Radek recognises the man's voice from the handful of times he has seen him and Jeannie together.

"Radek, I'm sorry. Jeannie's upset. I'm sure you understand. Look, the funeral is on Thursday. If you can attend, it would be good to see you and Anica there. I know Jeannie would appreciate it. I hope you and your family are well, Radek."

The message ends. Radek stares at the blinking screen for a moment, then bows his head.

Anica kneels beside him, reaching out to take his hands, resting in his lap. "We will go to the funeral. I will call your colleagues and explain."

Her words barely register. He nods, on autopilot, reliving his last conversation with Rodney in his mind.

"Radek?"

"I questioned his work," Radek says, suddenly. He has not told Anica all of his past, even now, when the details of the Stargate program are public knowledge. He spoke of Atlantis, but not of the loss. She does not know what Rodney attempted to do, only that the last time Radek saw his friend he returned silent and angry. But she listens. It is one of the reasons he fell in love with her.

"You argued?"

"Yes."

"You are not the first friends to disagree with each other. I am sure Rodney saw past that."

He isn't sure he can make her understand. "Rodney was extremely passionate about his work. He was determined. The last time we spoke, he believed he had achieved success. I disagreed."

"Not the first time?"

"No. But this time..." He sighs, taking comfort in Anica's hands, clasped in his own. "Rodney sacrificed everything for this project. I caused him to doubt his success. I am not sure he was thinking clearly."

"You do not believe he took his own life?"

"No." He says the word with certainty. No matter what the circumstances, he would never believe this of Rodney. But he realises now the self-destructive spiral Rodney began after Jennifer's death. The realisation comes too late.

"Radek?" Anica prompts.

"He may have been distracted. Even on Atlantis, if he was consumed in a project Rodney could miss meals or sleep. Perhaps... an accident, yes. A mistake." He closes his eyes for a moment, wishing he could take back his words.

"You are not to blame, Radek. You have described him as stubborn and obstinate. A man who would pursue a goal, no matter what. That sort of man would not allow himself to doubt, unless those doubts were already in his own mind."

Radek opens his eyes, and looks into the gaze of his wife. "Rodney was a great man. I wish things had been different."

"He made his own choices in life, Radek."

"I know. I wish I had been able to make him see..." He shakes his head. "Too late."

Anica kisses him on the cheek. "I am sorry, Radek."

Radek takes a deep breath, then gets up from his seat, reaching out to take Anica's hand.

"You cannot go back and change the past," she says, gently. "No man can do that."

He nods, sadly. Thinks of Atlantis, and all that has been lost. "Sometimes I wonder."