"Derek," Billy or was it Andy now, was standing in the doorway to Derek's room. They hadn't seen each other since escaping from the machines and Derek was more than willing to pretend that everything that had happened then was nothing but a bad dream, first because of Kyle's disappearance in the aftermath of their escape and now because his mind was still whirling from what Connor had told him.

Derek nodded for him to come in. Billy closed the door behind him but didn't come into the room, just leaned his back against the door, watching Derek's closely.

"Connor told you then," he said without preamble but it wasn't hard to guess what he was alluding to.

"How do you know?" Derek asked.

"I never really stopped building things," Billy shrugged but instead of Derek he looked at his feet.

"Does it work?"

"Did Connor tell you that story about Kyle and his mother?" Billy asked back.

Derek nodded.

"If you believe him then that's all you need, if not…"he looked up with the tiniest smile on his lips, "I can only tell you it works in theory. I can't proof time travel." Billy shifted. "How far is he sending you back?"

"20 years plus minus" He could see Billy calculating the date in his head.

"Derek, what I said…in that house…."

"You said nothing," Derek almost hissed. Just because he was willing to forget it, didn't mean the others would.

"You have to kill me." Billy said it calmly, rationally. As if this sentence had always been the conclusion to the conversation they were having.

"What are you talking about?"

"When you go back. You have to kill me."

"No." Derek answered instinctively. "If I do that you will die."

"That's what people do," Billy replied.

"Not you, not after all we've been through, I can't", Derek pleaded. "I could destroy it, your machine."

But Billy was shaking his head. "I'd built a new one. And another. I used to be quite stubborn."

Used to be? Derek mouthed and although Billy was smiling he shook his head again, "You will have to kill me. There's no other way."

"No," Derek repeated firmly. "Ask someone else. I won't kill you."

Billy crossed the room, sitting down next to him and taking Derek's hand between his.

"It has to be you," Billy pressed his lips to Derek's knuckles, "please, Derek," he whispered. "I don't want it to be anyone but you."

The question why was written all over Derek's face.

"I want you to remember me", Billy told him softly.

Derek tangled his hands into Billy's messy hair and kissed him. "If I kill your past self we will never meet."

"I know."

"I can't."

Billy's laugh is short and sad. "I'm not worth all of humanity. You know that. It'll be a better world. You'll have Kyle. You'll have a normal life. You will never miss me because you won't even know I ever existed. It'll be a better world", he repeated.

He couldn't, he shouldn't, "I'll do it," Derek leaned his forehead against Billy's, "I'll kill you." He blinked to keep the tears away and hid his face in the crook of Billy's neck. And if some tears slipped out under his closed lids then Billy never said a word about it. Instead he pressed his lips to Derek's head and whispered "Thank you." into Derek's hair.

/

"I want you to be there", was Derek's only request. If he was going on a one way trip to the past then he wanted Billy to be the last thing he saw from his old life. He whispered it between Billy's shoulder blades while his arms were wrapped around him, holding him close.

"Okay", Billy said.

Connor told him he would leave as soon as the current attack would end. The machines were firebombing the city ruins again to drive out the last scavengers hiding there and everyone kept to the bunkers and tunnels for the moment.

The knock came almost immediately afterwards.

"Derek Reese? It's time."

Suddenly he was overwhelmed with terror. He needed more time, but nothing would be enough. Nothing but a lifetime.

"I'll be there in a moment", he called when Billy pressed his hand reassuringly.

They got dressed quickly and Derek could feel his hands shake. He balled them into fists to hide it but Billy had already seen it. So he crossed the room and clasped Derek's hands, opened them until they were palm to palm with their fingers interlaced and Billy held them until they stopped shaking.

Derek drew a sharp breath and wanted to say something but set his teeth against it. Instead he leaned in and captured Billy's lips in a long and desperate kiss the kiss of two people who knew that they would never have another chance.

"I'll remember you", Derek said roughly and Billy ducked his head as if Derek had given him the biggest possible compliment.

/

The past was beautiful in a way he didn't remember it: shelter, clean water, fresh food and no machines out to kill him. And yet while he knew it was for the best Derek would exchange everything. Just to return to a filthy mattress in a windowless room when fire rained and most people were already dead.

Andy Goode was nothing like Billy Wisher. At least Derek didn't see it, or maybe he didn't want to see it. Andy Goode was the man he would kill, Billy Wisher was the man he had loved. He needed to distinguish between the two or he wouldn't be able to do it. He couldn't afford to remember Billy holding onto his hand and confessing who he was and what he had done.

He watched Andy going through his life, watched every move Andy made but he never simply walked into his house and shot him like he could have. Maybe should have, quick and clean and if he was honest with himself part of Derek didn't like the hesitation he was showing. Connor trusted him to get the job done, Billy too. Still, he waited.

And then someone burned down Andy's house and his computer with it. Someone was taking chances and if there was any justice in the world left, which Derek knew that there wasn't but Connor had always said that one should always hope, that would be it, Andy would give up and Derek could destroy the rest of SkyNet.

But as Billy had said, he was stubborn and Andy rebuild his machine this time even better than last if the meetings with his chess partner Derek listened in were any indication.

The tournament was the last straw. Despite everything, in spite of all his hopes the past enfolded exactly like Connor and Billy had told him it would.

Two shots, just to be safe and Andy lay dead on the floor and later, in his cell, it occurred to Derek that he couldn't go home anymore. With Andy's…Billy's death he had just irrevocably changed the future, his future. He was the only man left to remember Billy Wisher. And no matter if SkyNet would be stopped or not Billy Wisher was forever lost and Derek's younger self would never know what he missed by never meeting Billy.

Maybe it would be a better world but not for Derek. His world was long gone.

Kyle was gone.

Billy was gone as well.

He was alone.