Here we go again. I just can't seem to let go.

So, Martha Jones and the Doctor are at it again, and I won't lie to you: this is 50% ship fic, and 50% action/sci-fi/suspense or whatever you want to call it. At least as it is conceived at the moment. There will be squishy shippy moments, and there will be plenty of UNIT officers traipsing about where they shouldn't, people in peril, etc.

In any case, I hope this first chapter hooks you. And one more thing... wait for it...

Leave a review!

Enjoy!

ONE

Every morning before her shower, Martha Jones slipped off her engagement ring and set it in a crystal ash tray that had been her grandfather's. She would, mostly involuntarily, contemplate her fiancé who was currently in the jungle, trying to help Ugandan refugees' children in the Congo. She would smile wistfully and wonder just what he was up to at this moment. Then, she would step into the shower for a few minutes, step out again cleansed, return to the night stand and slip the ring back on. She would make sure it had returned to the third finger of her left hand before she even unwrapped her hair from the towel, or put on her fuzzy seafoam green slippers.

Today was no different, except that she took a little extra time in the shower. She had to pay extra attention to waking up. She massaged her scalp more than usual, and frankly turned the water temperature down just a bit, to keep herself from getting too cosy in the steam. She was more than just a tad sleep-deprived, after the run she'd just had. She had wanted to lie down and crash the night before, but her thoughts had been racing, and she hadn't been able to get settled.

Yesterday, she had used her new mobile phone to ring her old mobile phone, and summon the Doctor out of who-knows-where. He had come when called, of course. He and his new Companion, Donna, (she tried not to think of Donna as her replacement) had joined her and the rest of the special squad with UNIT at the ATMOS distribution plant, and had discovered Sontarans working against them. The potato-shaped aliens were basically trying to choke the Earth with poisonous gas, so that they could use the planet as their cloning base.

And then, for some "timey wimey" reason that she did not understand, while she was inside the TARDIS saying her goodbyes, the vessel had locked them all in and taken them to a planet called Messaline, sometime in the future. Apparently, it was all to do with a pretty blonde who was eventually nicknamed "Jenny," and had sprung from a machine that grew her out of the Doctor's skin cells. With all of the crazy things she had seen with the Doctor, that had been one of the strangest and most disturbing. And that was quite apart from the blonde herself calling the Doctor "dad."

For her part, Martha spent most of their time on Messaline separated from the Doctor, Donna and Jenny, trying to find her way back to them over the treacherous, windblown surface of the desert they were in. She had befriended a native Hath, and then watched him die as he tried to rescue her from a quicksand-like pool of something. The experience had hit her harder than she would have thought.

Both adventures had seen a lot of death of innocents, a lot of senseless fighting, a lot of aliens being strangely drawn to Martha, and a lot of the Doctor having to take the bull by the horns, in order to get anything accomplished. After two days back in the Doctor's world, she was ready to come home and continue waiting for her fiancé, and keep plugging along at her job with UNIT. She was done with all that. She was exhausted. She was emotionally drained. She was ready for a new day to come.

So why hadn't she been able to sleep?

Because, damn it, the Doctor still had that power over her. She had walked away from him because of it, had got engaged to a very nice man, even, and yet…

She had tossed and turned, angry with herself for dwelling on it, but unable to shake it off. He had looked amazing in that blue suit. He was styling his hair a bit differently these days and she liked it. He had made her heart flutter with his cleverness and self-sacrifice, and the fact that he rescued her from the cloning source support system, and gave her his coat to wear. And had she, or had she not, seen a distinct flicker of jealousy when she'd flashed her engagement ring? Or was he just experiencing a narcissistic deflation because it appeared that she was no longer hung up on him?

After two years of feeling restless and unfulfilled over the Doctor, deciding enough is enough, and nine months of getting on with life, she was back in that place. Once again, she had found that she couldn't get the bloody Doctor off her mind, and it was keeping her awake at night.

And so, in the shower, groggy, slow, surely on a path that would lead to being late for work, she cursed him. Him, and that hair, and those eyes and that tight suit (which had to be a ploy, it just had to! How could he not be doing it on purpose, when he put that suit on every day?) She shut off the water, wrapped herself in a towel and went about her routine like a zombie.

But when she finally walked out the front door, twenty-two minutes later than usual, her ring still lay in the ash tray on her night stand.

With the dread of post-Sontaran paperwork pervading her every pore, she threw open the door of the secret entrance to UNIT, and placed her left hand on the print pad for verification.

"Shit," she sighed, noticing, at last, the absence of her engagement ring. She clenched her teeth and shook her head; she knew it was no coincidence that she was harbouring the Doctor in her brain today, and had forgotten to don that most palpable of reminders that she was supposed to marry someone else. She could tell herself that it was because she'd been tired and off-her-game today, but… why was that exactly? Who was she really kidding?

"Martha Jones, M.D.," a robotic voice said as a green ring of light surrounded and scanned her hand. "Entering secure facilities at eight twenty-two, Greenwich Mean Time. Good morning, Dr. Jones. You have one new message from Colonel Mace."

Her work station was a standard clinical exam room with an adjustable exam table covered with a long sheet of butcher paper. There were two chairs and a counter along one wall with a computer, a phone, a sink, and a few of Martha's personal effects. In the cupboards below the counter was where medical instruments were stored, mostly meant for evaluating human beings, but a few of them meant for examining sentient creatures, not of this Earth.

Her plan was to set down her rucksack, then go find a cup of coffee in the central work room, then see if the sound-proof computer centre was available today, as she did not feel like sitting on her round, rolly stool to write her report on the Doctor and the Sontarans. But first, she checked her voice mail as she knew there was something new from the Colonel.

"Dr. Jones, it's Mace. When you arrive today, please come see me in my office. It's about the Doctor."

She sighed. What had happened now? she wondered. She went through the semi-hidden door at the back of the exam room, turned right and found the central work room just a few doors down a narrow corridor. She extracted a mug from the above cabinet, and poured herself a cup of surprisingly fresh coffee. She took a few sips before stepping out through a different door into one of the main hallways, and taking another right to find Colonel Mace's office.

"You wanted to see me, sir?" she said, walking in without knocking.

"Yes, indeed, Dr. Jones," he said, looking up from his laptop. "Please have a seat."

She did. She gave him time to finish whatever he was doing, and true to his efficient, polite form, he did not make her wait long.

"Right then," he said. "Thanks for coming."

"No problem. What's up? You said it was about the Doctor?"

"Yes," he said. He turned to his right and opened his desk drawer. When he turned back toward her, he was holding a rectangular object, about the dimensions of two Rubik's cubes stacked on top of one another. It was gold, and had familiar designs carved on it. He set it on the desk away from himself, but right in front of Martha. "Do you know what that is?" he asked.

"I recognize the patterns," she said. "It's Gallifreyan lettering."

"It is," he confirmed. "Though none of us has any idea of what it says. I don't suppose you would."

"No, sorry."

"Well, no matter," he dismissed. Then he took a deep breath and rested his forearms on the desk, leaning on them to talk to her. "Dr. Jones, this box was entrusted to us by the Doctor in the 1970's."

"Really?" she asked, genuinely surprised.

"At the time, he was in his third incarnation, I believe, and he was working for us almost full-time."

"Right, because he was banished to Earth."

"Yes. Initially when we received it, we put it into the care of Miss Jo Grant, a UNIT operative who worked closely with the Doctor, and travelled with him on occasion."

"Yeah, I know who she is."

"Well, UNIT thought she would be the best person to look after the item. When Miss Grant left UNIT, it was passed to Brigadier Lethbridge-Stewart."

"Didn't I hear you say that he's in Peru?"

"Precisely why it was doing no good sitting on the mantelpiece in his parlour at home," said the Colonel. "And anyhow, you've a closer relationship with the Doctor than the Brigadier has these days. When I phoned him last night, he said he wanted it passed to his daughter, but when I explained who you were, how you came by your position, and your history with the Doctor, well… he agreed. It is now in your care."

She frowned. "Well what the hell is it?"

"It's called the Eustarus… the Doctor named it that. It's a Gallifreyan word that means, roughly, fail-safe."

"Okay," she said, waiting for more info.

The Colonel took a deep breath and began to explain. "In 1973, the Doctor ran afoul of another Time Lord called Omega. That's thirty-five years ago. To us, that is. On the Doctor's timeline… well. As I said, he was in his second regeneration at the time – his third body. The Doctor that you know, well, I believe, is in his…"

"Tenth," she finished.

"Yes. So centuries have likely gone by. Anyhow, Omega was a Time Lord – and from what I understand, a really chuffing clever one, at that. He is – or was, for a time – revered almost as a god, along with another Time Lord called Rassilon. The two of them conducted experiments in time travel that really helped to push forward Gallifreyan technology. They were pioneers."

"I'm sensing there's a but."

"Indeed. Omega's cleverness overwhelmed him in the end. He had forged a device that could control the physical reaction inside of a star, and he thought he could harness it to power his time experiments. But his tampering caused a supernova, and he was pulled into it, and presumed dead. That is, until the Doctor found him alive in an anti-matter universe."

"An anti-matter universe? Did I just hear that correctly?"

"You did. How much do you know about physics and astrophysics?"

"A bit."

"Well," Mace said, actually chuckling. "Then you're one up on me – I don't understand a bloody thing about it. Maybe someday you can explain it to me. Anyway, apparently, it's possible for a supernova to turn itself inside-out… to stop expanding, and then, in fact, contract in upon itself and become… well, essentially an anti-supernova."

"Also known as a black hole," Martha told him. Then she shook her head, as if to shake off a fog. "Wait, are you saying, he's trapped in a black hole?"

"Was," Mace answered. "But not exactly in a black hole. Apparently the pressure of the black hole's gravity was such that it pushed him through some kind of barrier into a different universe… one of anti-matter. And that is where he was trapped, that is, until he touched the Doctor's flute."

"The Doctor's what?"

"The Doctor used to play this pipe-flute thing… I don't know what it's called. It was in one of his very early incarnations. Omega touched it, and, as it was the only thing around him made of matter, it destroyed the anti-matter universe. I don't know how it all happened, exactly – I just read the file last night, and the explanation… well, it wasn't written by a Time Lord. It's sketchy at best."

"So, Omega himself is destroyed."

"I believe so, yes."

"So what's the fail-safe thing all about, if Omega is destroyed?"

Colonel Mace took a moment, and his voice lowered by a few tones. "A Time Lord, as I'm sure you're aware, Dr. Jones, is a powerful being."

Her heart fluttered a bit, and she cursed herself internally. "Yes, I'm aware," she croaked, her mouth having gone dry. She cleared her throat then, and listened further.

"Not only have you spent a good deal of time with the Doctor, but I'm told you've also met the Master."

She chuckled. "Met the Master. Right."

"Saved the world from him, if I'm not mistaken."

"Yeah," she whispered, pulling her hands into her lap and gazing at them. She had no wish to revisit anything about that time in her life.

"The planet owes you a debt of gratitude, Dr. Jones."

"Yeah, too bad it never happened."

"As long as there's UNIT, and there's the Doctor and your family, it happened. Our records show that the Doctor turned back time and erased…"

"Colonel Mace, I'd really appreciate it if you could tell me what any of this has to do with the gold box." She touched its top lightly, with her index finger.

He cleared his throat. "Yes, of course. As you know, the Doctor has never been a stranger to the idea of a rogue Time Lord. He's come face-to-face with the Master countless times. Omega was on a different scale altogether, and after that whole debacle, the Doctor was a bit shaken. He became terrified of his own nature, his own power and cleverness, his own potential for… well, evil."

"I see," Martha said, nodding sobrely.

"He devised the Eustarus, a fail-safe, in case he himself ever…"

"Went all Darth Vader?"

"Pardon me?"

"Turned to the Dark Side."

"Yes. And given the forces he meddles with on a daily basis, it would not be out of the realm of possibility."

"I suppose it wouldn't," Martha agreed, though she could not imagine a world in which the Doctor wasn't on her side.

"Of course, at the time, he'd never have guessed that at any point he'd be the Last of the Time Lords save for the Master. But even back then, he didn't feel he could trust them to put him back in line the way he felt he needed to be. He said the Time Lords were dogmatic and rigid on the whole…"

"Yeah, he's told me the same thing," Martha said. "He probably thought they'd try to reshape him in their image, rather than turn him back the way he was. Is."

"Or worse, try to use him for something in his, if you will, darkened state."

"Blimey."

"Apparently, they tried to do that with the Master once."

"Seriously?"

The Colonel nodded. Then he took a deep breath and mused, "What I can't work out is why in the world the Doctor never used a device like this on the Master."

"No," Martha said. "He'd never do that. It would be an empty victory to him. He'd want the Master to decide to revert to the side of good, because he got hold of some vestiges of real good within himself."

"Well, whatever," said Mace, uncharacteristically. "Time Lords will be Time Lords."

Martha already knew that the Colonel disapproved of some of the Doctor's ways, in particular his peacekeeping ways. Needless to say, Martha found those ways rather beautiful, and Mace rather difficult at times.

"In any case," Mace continued. "Only humans, according to the file, could be trusted to help turn the Doctor back into the lovable scamp he really is, but he knew that humans would not have the means to do so. He knew that if he ever turned inside-out on himself, he'd do everything he could to stomp on any resources that Earth might possess that could possibly stop him. So he forged this."

"Couldn't he just come and take it, if he went bad?"

"He thinks it's in a vault inside the Tower of London," the Colonel said. "No-one ever told him that we sent it home with the Brigadier. We reckoned that if he ever went for it, it would give the Brig a head-start to activate it."

"I see. So I'm to take it home, and never let the Doctor know that I have it."

"Exactly. Are you comfortable with that?"

"I guess."

"Dr. Jones, I'm going to need an affirmative."

"It's fine. Yes. Affirmative" she said. "I'm comfortable with it." It was a slight lie – she was not entirely comfortable with it. But, she thought, it would be better than someone else having it. What if the thing was dangerous?

"Good, I'm glad to hear it," Colonel Mace said, with a slight hint of a relieved smile.

"How does it work?" he asked.

"For that, you'll have to speak with our physics department," he said. "They're expecting you in an hour's time. Ask for Dr. Fortis, and he'll give you all of the details. Because I've no blooming idea. I've even read that section of the file, and I still don't know."

Martha held the Eustarus in one hand, went through a thrice-reinforced door, and flashed her badge at the security guard. "Dr. Jones, here to see Dr. Fortis."

The guard grunted and nodded, and she walked past him. She knew that security was tight in the physics department of UNIT for good reason, and that the thugs in charge of keeping the place safe meant no disrespect. They were simply trained to be stony-faced and unflappable.

Dr. Fortis, on the other hand, was anything but stony-faced. "Dr. Jones!" he practically shouted as she walked into the gigantic laboratory space. He rushed at her and grabbed her hand to shake it vigourously. "It's such a pleasure to meet you!"

Dr. Fortis was lanky, rather unkempt with longish, wavy dark hair and glasses that sat crookedly on his face. She found him disarming, and smiled. "Likewise, Dr. Fortis."

"Please call me Lawrence," he said. "Or Larry if you like."

"Okay," she said, "Larry."

"Forgive me for being such a zealot. I'm just such a huge admirer of… well, the man we're here to discuss. What was it like working with him?" He stood just a hair too close to her, holding his arms folded tightly in anticipation of her answer.

"Erm… well…"

"I mean it must have been wonderful!"

"Wonderful, yes. But also…"

"Terrifying."

"Yeah," she chuckled. "Come up with any adjective you can think of, and I can almost guarantee that it perfectly describes the experience of working with the Doctor, as you put it."

"Amazing?"

"Yes."

"Dizzying?"

"Yes."

"Explosive?"

"Yes, listen… can we just talk about the fail-safe? I actually have a long day ahead of me. That amazing, dizzying, explosive and occasionally terrifying man, and his Sontaran mates, have left me with quite a lot of paperwork to do."

"Of course," said Fortis, clearing his throat. "Follow me, please."

They walked across a relatively short span between the door and a long work table. The lab was the size of a gymnasium, and bustled with people in white coats. Some experiments occurred here, but, Martha knew, most of it was examination of alien technology and physical principles, and advanced mathematics calculating things like the mass of dimensional portals.

And, apparently, working out stuff that a Time Lord put in a box thirty-five years ago.

"So I assume that Colonel Mace explained to you where that little gem came from," Fortis said as they walked, gesturing to the gold box tucked under Martha's arm.

"He explained how and why UNIT came by it, and who made it, but not how it works," she told him. "And I would guess that if I'm supposed to take it with me, I'll need to learn what it does."

"And how to activate it."

"Right." Martha seriously doubted she would ever have to do that, but she resolved to learn as much about the Eustarus as she could. She didn't want some kind of ticking time-bomb just sitting on a shelf in her wardrobe.

He slid onto a stool and gestured for her to do the same, across from him at the work table. He pulled a pile of papers from its position on his left, and centred it in front of him. The bundle was labeled The Doctor, and Fortis smiled sheepishly. "Part of his file."

"Part of his file?" Martha asked, gaping. "Colonel Mace also mentioned part of his file. How bloody big is the whole file?"

"No-one knows," Fortis shrugged. "It's never all in one place at the same time, as there is no digital copy. Pieces of it are everywhere throughout UNIT. Everyone seems to need something on the Doctor at any given moment…"

"Why is there no digital copy?"

"Because then the Doctor himself could access it," said Fortis, winking at her.

He pulled a page that had been marked with a pink sticky note from the middle of the stack, and tried to open the rest of the file like a book so that nothing would be out-of-place. He pulled a pen from his breast pocket, and on the pink sticky note, he scrawled something, then handed it discreetly to Martha.

"This is the code phrase that activates the Eustarus," he said. "Memorise it, then burn that piece of paper."

"Gotcha."

"As you might have already surmised, the Eustarus is sentient, and can, in effect, hear you."

"Oh, wonderful."

"Well, don't worry," he said. "We've examined the thing within an inch of its life, and you can trust me when I say that it's not listening all the time. Oh, we were mightily paranoid about it in the seventies and eighties… was it a surveillance device? What if it fell into the hands of the Russians?" Fortis laughed. "But it's not anything like that. Something about that phrase awakens a kind of mind within the device."

"All right. Then what?"

"As we understand it, a button will appear at the top, and all you've got to do is press it."

"Simple as that?"

"Simple as that."

"What will it do to the Doctor?"

"Now, that's the not-so-simple part," Lawrence Fortis said, adjusting his glasses nervously. "Did Colonel Mace tell you that this whole thing was inspired by the Doctor's run-in with Omega?"

"Yes, he did."

"And did he explain who Omega was, and why and how the Doctor had to deal with him?"

"As much as he could, yes."

"Well, when he was conceiving the Eustarus, the Doctor used the principles of astrophysics – specifically, a parallel of what happened to Omega with the supernova and the black hole – to create a vortex, as it were, that will invert concepts rather than matter."

Martha's jaw dropped. "Excuse me?"

"I know," Fortis laughed again. "How's that possible, right? How can anyone be that clever, right? But the Doctor is!"

"Yeah, I know that," she dismissed. "But, you're saying that this thing can, what? Grab hold of something intangible, like a concept…"

"Like the Doctor's thoughts, tendencies and behaviours…"

"…and catch them in a miniature supernova, collapse them into a black hole and push them through into antimatter?" She pointed at the gold box. "Are you saying that this little rectangle can perform an extreme miniature gravitational collapse, with the Doctor's evil ways inside?"

"Is that so unbelievable?"

Martha had no idea what to say.

"And that's not even the end of the story. After it does all of that, it essentially spits pieces of the Doctor's psyche back out again, to put it in touch with what the file calls standard reality."

"What the hell does that mean?"

"Just as Omega's touching of something made of matter confused the anti-matter universe enough to destroy itself, the Doctor's intangible 'parts' coming into contact with another person's intangible 'parts' will cause the Eustarus to be destroyed and the containment to fail. The Doctor is then free, essentially. Either he's reverted or he's not."

"So one would better bloody well hope that someone is nearby that the Doctor's psyche, or whatever you just called it, can hold onto, otherwise, the miniature astro-reaction dissipates, its gravity fails, by design, and the Doctor is still evil."

"Yep. You have a magnificent sixth sense for these things, it seems."

"So this is why you need me, or Jo Grant, or the Brigadier."

"One of the reasons, yes. And that was clever on our parts; I don't think even the Doctor himself anticipated that little tidbit. He designed it just to latch onto whomever, but upon inspection, some of my UNIT predecessors determined that having a familiar 'soul' nearby would help the process to be more complete."

Martha shook her head. "This is madness. It's just… madness."

Fortis shrugged. "Yes, and no. Omega worked out how to remotely control the physical reaction inside of a star. And if you ask me, the Doctor is every bit as clever."

Martha looked at the box, her eyes as wide as saucers. "And, wherever he is in the universe, this thing can find him?"

"If this file is to be believed, yes," said the physicist. "The Doctor forged it himself. Who better to know how to track down the Doctor's energy signature across galaxies and the time vortex?"

"I suppose," Martha said absently, staring into the intricate golden carvings on the surface of the box. Then she asked, "Would it hurt him?"

"It traps him, if only temporarily, in a localised, miniaturised pocket of hypergravity. I can't imagine that it wouldn't hurt."

She gulped, nodded, and continued to stare into the surface of the device.

Lawrence Fortis just let Martha Jones stare for a few moments, and come to terms with what she had heard. He could imagine the wheels turning inside her formidable mind, the absorption of the idea that an astrophysical reaction was waiting just there, inside the thin walls of the Eustarus, sitting before her.

After a few beats, he said, "Dr. Jones?"

"Hm?" she mused. Then she sat up straight. "Yes?"

"I have another document for you," he said, shyly pushing a blue sheet of paper across the space between them. "This cannot be photocopied nor photographed – the text would not show up. Please memorize the text as soon as possible, then burn this document as well."

She squinted at it, then read aloud, "'Outside of the ninety-hour window before or after regeneration… extreme change of attitude or opinion, accompanied by embellishment and/or accessories to the change. Extreme anti-social behaviour or overtly social behaviour. Undue fatalism, resulting in destructive action. Insidious manipulation of large-scale channels of power or control.' And it goes on from there. What is this?" she asked.

"These are symptoms," said Fortis. "Signs to look for."

"Signs that the Doctor has gone over to the dark side?"

"That he's gone all Darth Vader, yes," Fortis said with a nod.

Martha smiled.

"But these are 'symptoms' that the Doctor exhibits all the time," Martha protested.

"I suppose that's why he puts modifiers in, like extreme, and overtly. Undue, insidious."

"It's all subjective!"

"Which is another reason why they decided to entrust it to Jo Grant all those years ago, and then the Brigadier. They want someone who knows the Doctor, not just a team of so-called 'experts' who have read up on him. You've spent time with him, you care about him, you've observed him, so you'll know when his fatalism is undue. When his manipulation of large-scale power becomes uncharacteristically insidious. You'll know if changes in him become extreme, or overt, and will recognise an 'accessory' to those changes."

"That's giving me a lot of credit."

"You deserve a lot of credit, Dr. Jones."