The Doctor didn't look up when Sam came back into the TARDIS. He was busy quadruple-checking his findings. If he was right—and he really, really, never wanted to be wrong more than he did now—then he didn't have time for small talk. Didn't mean he wouldn't keep it up. Just that he…might need to be a bit more…brief than usual. Which would be difficult with Sam, because Sam was the type of person who would ask questions, and he would even manage to ask the right questions some of the time, and the Doctor would want to answer him properly, but he didn't have the time to do that now, because any explanation he gave would prompt more questions, and—

"I told Al."

"Good, good." The Doctor hit a few more keys, impatient. He had the distinct feeling that he was running out of time. And that…was never a good sensation for him.

"They still had trouble keeping a lock on me," Sam continued. "It worked for a minute or so, and then there was some sort of interference. It settled down again; I thought it meant that you were able to boost the signal."

"Yeah, managed that." The Doctor twirled a dial, filtering the data on the screen in front of him, searching out different patterns. "But, yes. Those chronon strands I was talking about before? Positively saturated in artron energy. Bound to cause some temporal interference. You would've had a moment's grace at first, before everything settled, before things had a chance to react. Well, I say a moment. You could have had only seconds. Less. Or more. Hours, years. Depends, really. The effects aren't necessarily the same twice."

"Due to natural fluctuations in the time stream or the unique circumstances of every situation or—?"

"Bit of everything, really. Can't explain it properly now, sorry. Just need to be sure." The Doctor tried reversing the feedback, just to see what he could get.

"About?"

"The…whole…situation. Current situation." No results there. Maybe if he recalibrated the—

No. Who was he kidding? It wasn't going to change. He'd run the data every which way. He needed to face the facts. Even if he didn't particularly like them.

A beep confirmed his suspicions. Well, he'd hoped. And wished. But, as they say, if wishes were horses…. Still. Had to make the best of it. Had to try. Had to…to…hold on, what was that? That made things a whole lot…. That…that…. "Oh, that's not good." The Doctor frowned. "That's not good at all."

"What is it?"

"Oh," the Doctor said lightly, shaking off his expression and waving Sam's question away with one hand. "Not much, really."

"Doctor."

"Well, it's just that…. It seems when the denaturing occurred, and the strand diverged into two parallels, there was a slight…." the Doctor trailed off, catching sight of Sam. Contrary to the blatantly baffled or slightly glassy-eyed expressions he was used to seeing on his companion's faces during his explanations, Sam seemed to be drinking in every word. He'd done that last time, the Doctor recalled. It had been very hard to lose him in an explanation. It had been a relief, then—proof that the entire planet wasn't populated by stupid apes, as his ninth regeneration had so loved to believe—but now, well…. Now, he would have preferred having a companion who could be fooled by what he was about to say.

After all, it was a lot harder to protect people when they knew precisely how much danger they were really in, and when they had enough knowledge to begin acting in a way that they considered appropriate and which, in other similar circumstances, very likely would be appropriate, but for the current set of circumstances they were in now, would most definitely not be appropriate.

The way things seemed to be going, Sam's good intentions would just make things worse for him.

"How should I put this?" The Doctor rubbed the back of his neck, not really looking at Sam. "There's only the one of me, I said. But I'd never been to the Project until I met you. And now you've leapt into me prior to that time. Which means that's changed."

"Not necessarily," Sam countered reasonably. "I know they've been working on the system, trying to make it so the leapee, when placed back int—"

"No," the Doctor cut in. "That's what Al said, and what I told him still stands. That primitive bit of trickery doesn't work on me. Especially when you haven't perfected it." More to himself than to Sam, he added, "Timelines are nearly twisting more now than they did with Donna."

"Then what are you trying to say?" Sam asked, now sounding worried.

"I'm…splintering. And…that's going to catch up with me." The Doctor ran his fingers through his hair and looked at Sam. "Probably very soon."

"Splintering," Sam repeated, his mind conjuring up all sorts of consequences. And somewhere, the Doctor knew, he had an inkling of the true weight of the word. Of everything it meant.

"Splintering, fracturing, cracking, what have you," the Doctor confirmed, his tone grim. "Because you, Sam Beckett, went back and changed my timeline. Oh, I'm not blaming you," the Doctor added hurriedly, catching the horrified look on Sam's face. "Not when you still don't know how your leaping about really works. Just saying…well, just saying that I need to act quickly. Before it…ripples down to me. And what happens…happens."

"And what's going to—?" Sam stopped. The Doctor had turned his head, looking at the door beyond the console room with an expression of mounting horror. "What is it now?"

"What have you told Martha?" he demanded, rounding on Sam. "What did you tell her?"

"I…sort of let her make her own assumptions," Sam admitted. "You may know all about me, but I don't remember you. She knew something was off, and she finally confronted me about it, and…." Sam shrugged. "I think she thinks I'm a different personality of sorts. She wasn't making a lot of sense. Kept mentioning a John Smith like he was distinctly different from you."

"Oh." The Doctor's lips tightened. "Right. He was, in a way. Though I'm everything he was. But if that's what she thinks you are, then.…"

"I did tell her my name," Sam admitted. "But not who I really was."

"You may have to, before we're through. We'll play it by ear. I'd rather avoid it if possible—traces and all—but sometimes things just…c'mon." The Doctor was back at the controls of the console. "C'mon, c'mon, you can shift it here, I need it. No, don't argue with me, old girl, I don't have a lot of time, and... Yes!" The Doctor backed away from the console abruptly. "If you need me, I'll be in the secondary control room. Martha hasn't found it yet, I don't think. And when she comes in here, just after I've gone, don't worry. She won't have seen me. I…tweaked a few settings." Flashing Sam a grin, he bounded through the interior door and deeper into the TARDIS.

The Doctor hadn't moved much since she'd left him, Martha thought. Though, to be fair, he wasn't really the Doctor. He was no more the Doctor than John Smith had been. He was a completely different person, human, and the Doctor was buried in there—more or less. What she didn't understand was why this Sam Beckett knew that. John Smith certainly hadn't. He'd been faced with the truth and hadn't wanted to believe it. Not that she really blamed him, when it came down to it, and he had made the right choice in the end.

"Doctor?" she asked, biting her tongue the moment she'd said it. Of course not.

"Yes?" he asked, turning round to look at her.

But it wasn't him. It was still Sam. She could see it now. She knew what to look for. "I was…hoping he'd be back," she mumbled.

The Doc—Sam glanced behind her to the door she'd just come through. "Not yet, exactly," he admitted. "Haven't made much progress. I still don't know what I'm here to do."

The way he said it struck Martha as odd. To her, it sounded like this…persona, for lack of a better word, of Sam was there to do something that the Doctor couldn't. And she wasn't sure she could name something that the Doctor couldn't do. Whatever it was, she wasn't sure she wanted to know.

But if she didn't do something, she'd never get the Doctor back. Not really. "What can I do to help?" she asked. "I mean, there may not be much, but every little bit, as they say."

Sam sighed and levelled a gaze at her that was eerily like the Doctor's. "Time's dividing," he said simply. "It needs to be mended."

"And you can do that, yeah?" she asked. "With…help?"

"I hope so," he answered. He expanded on his explanation, continuing, "The timeline's split into two parallels. They're nearly identical, but not quite, and we're not on your parallel, not now. Not as I understand it."

She'd almost slipped into the mode where she nodded and agreed until he stopped briefly, at which point she could ask him again and he'd give her the simpler version, but then he tacked that on, and it jarred her. "What do you mean, not as you understand it?" she asked. "Doctor, if there's someone else who's—"

"It's Sam," he corrected gently. "And, yes, it's all second-hand information. From…my help. Because right now, I can't…. I can't figure this out on my own."

She walked over to him now, struck by how lost he looked. "It's okay," she said, glad her voice wasn't quavering, because she was sure finding it hard not to cry. "That's why I'm here."

He smiled at her, saying, "Thank you."

She didn't know what she was getting into, and she didn't know how she'd come out of it, but she knew that, no matter how horrible things got, she'd never regret her decision to travel with the Doctor. She couldn't imagine leaving, not yet, but someday…. She would, some day. She wanted to become a doctor, after all. She couldn't throw that away.

But now the Doctor needed her, and she wasn't going to let him down.

The Doctor closed the door behind him and just stood there. He hadn't been in this room in a long time. Well, by human standards, at least. By his standards, it hadn't been that long at all. Granted, by his standards, he was a lot younger than he should be, considering he was on his tenth regeneration.

On the last leg of his tenth regeneration.

Of course, he didn't really count how old he was. For one thing, life as a time traveller was complicated, though that's to be expected. For another, he wasn't entirely sure that he wanted to know. The only people who asked these days were humans, and most times he was happy to let them make their own assumptions. There had been a few times when he'd announced an age simply because the gravity of the situation had called for such a thing, but, honestly, he knew he'd seen more than a measly nine centuries. He just wasn't about to tell anyone that. Because even if he was young by Time Lord standards, he felt positively ancient next to humans.

And no matter how much he thought to avoid them, he kept coming back to them.

Donna was right. He needed someone.

But Martha was also right. Oh, he'd known what she'd said. The TARDIS had picked up on it, through the energy clinging to Donna and the residue that still saturated Martha. She'd said what Donna had already known and had been willing to discard: that he was dangerous. Oh, it didn't appear that way, and he meant well, but he was dangerous.

Donna had learned that lesson. The hard way.

And then he'd made her forget it. Every single thing.

And it tore him to pieces.

All of them did. Donna, Martha, Rose...even Jack and Mickey, which was a surprising and slightly disturbing thought. But his sorrows weren't limited to this regeneration, oh no. There had been many, many others. Adric. Sarah Jane. Barbara. Jamie. Jo. Tegan. Ace. Grace. Leela. Zoe. Ben. Nyssa. Harry. Peri. Polly.

Romana.

Susan.

River.

And the list went on, and he'd be there for hours if he named every one of them. But he didn't need to name them to feel them in his hearts. And there were so many others whom he'd simply encountered, but whom he'd touched, and sometimes…sometimes his presence hurt them instead of helping them. Some days, despite his best intentions, people died.

Most times he tried to prevent it. Sometimes he allowed it. And sometimes he caused it.

He'd nearly lost track of time again. Well, not really. But still. He'd spent far too much of it reminiscing, berating himself for things that couldn't be changed, and he needed to focus on the task at hand.

Sam needed him. An entire parallel needed him. Two, actually, because if he didn't figure this out, the termination of one would cause the eventual preliminary destruction of the other. But, simple answer. Splicing. Easy peasy. Easy as pie. Piece of cake.

…With two Time Lords. Each with the proper equipment. And preferably a third, given how tricky the process was, what with the scale of it all.

The Doctor sighed, pushing his sorrows aside. He really did not have time right now. Especially since he could feel that first crack that signalled the splintering. Perhaps that was why he'd allowed himself to be momentarily overwhelmed by memories and grief and pain and joy. But that didn't matter now. One little crack, well, it wasn't much. He could ignore it. If he concentrated.

Though it was a bit like having an itch that couldn't be scratched.

Still. Timelines to be preserved. And the damage was accumulating. Rather quickly, actually—more quickly than he'd like. The splintering only compounded matters, what with the parallel due to terminate and him being stuck on that parallel and Sam here to—

No. He wouldn't let him. Which was precisely why he hadn't told him. He'd find a way around it. He had to. His life depended on it. Sam's task—he could call it a task, couldn't he? That was close enough, wasn't it?—wasn't to keep him away, oh no. Sam was the one leaping around for good. And no good would come of ensuring that the parallel ended, especially since he'd probably leap out and the Doctor would find himself….

But that's what the splintering was, in a way. An ending. One way to nip it in the bud, that splintering, if he let this happen. But that made no sense. Sam's leaping was the reason the splintering had begun; his leaping in had caused it, so it wouldn't make sense that he would have leaped in to end it. It, and the rest of the parallel. And possibly him, if he didn't play his cards right. Thing was, he wasn't sure he could, not like this.

Which meant that he was right, and the initial interpretation of the data was wrong. Sam was here for a different reason, not to ensure the destruction of a parallel and everything on it, him included. Things weren't supposed to go that way. Oh, he knew. Besides, there hadn't been any knocking. Surely the knocking would have been heard when he first came. Right?

Because this would mean death, if it happened. Not regeneration. There'd be no time for it.

No.

Sam was not his executioner.

"What am I missing?" he hissed. He'd scanned fluctuations in the Vortex stability, cross-referencing it with the strength of the chronon strands. He'd needed to do that to confirm that they were in a pocket. Running the rest of the tests had been routine, a necessity for information confirmation, but this time, the basics didn't cut it, not for this. But everything else tended to take a bit more time than he had to spare, and he couldn't afford to start down the wrong path.

But neither could he afford this internal quarrelling. He needed to keep focused. He'd reviewed the basics ten times over. Now, he needed to find the most probable possibility. That, of course, required more tests than he had time for. But, he was clever. He could make it work. He had to.

Grinning with something that was more grim determination than humour, the Doctor went to work.

"Dr. Smith," Gooshie asked carefully, "may I ask why you feel it necessary to review all of our records?"

"Course you can."

The Doctor did not continue, and Gooshie belatedly realized what the humour in his answer had meant; the Doctor had been literal and was waiting for Gooshie to rephrase his question and repeat it. He recalled the day Ziggy had gotten into one of those moods, despite her insistences of being above that sort of thing, seeing as she was a computer and therefore technically did not have moods, since having moods implied having feelings. Work had been…less than pleasant that week. "Why do you insist upon reviewing our records?" Gooshie repeated.

"Oh, you know," the Doctor answered, waving a hand around him. "All this. New to me. Haven't run across it before. Which I find surprising, really. Brilliant, and I have to commend you for it, but, blimey," he looked over at Gooshie, tearing his eyes away from their records, "you do realize that Sam Beckett could have torn himself to pieces and taken this entire base with him, right? And if things had gone catastrophically wrong, he risked terminating the timeline, and without so much as a moment's notice." Then the Doctor grinned. "But he didn't. In his brilliant, bumbling way, he avoided that without even knowing how likely it was to happen. But if I'm to understand everything I can about this Project," he continued, his tone slightly more sombre now, "I need to know everything you've done." He flicked his eyes back to the computer screen, opening and scrolling through a few more reports faster than Gooshie could even think to read them. "And now I have. At least, the official part. But that'll have to do for now, I think."

"And wh—"

"But, you know, the thing is," the Doctor continued, cutting Gooshie off, "if I, well, he, thinks that this is a Type LXXVI parallel, then that means he'll have come up with a preliminary hypothesis as to why Sam leaped in there. But I can't imagine that it would be a very pleasant one. So all that is is really his way of telling me to look through and see if I can find out anything from this end, since where he is, his hands are tied. But he wouldn't do that unless—" The Doctor, who had been rambling at a hundred miles an hour, stopped.

"Unless?" Gooshie prompted when the Doctor didn't continue.

The Doctor looked at Gooshie, eyes wide with horrific realization, Sam's hair looking dishevelled beyond recognition, the blood drained from his face. The expression was one of disbelief and denial of an impossible truth that nevertheless had to be accepted. Gooshie had seen that look on Dr. Beckett's face once before, when he'd had to tell Sam Beckett that he would be shot in less than an hour and that they still hadn't tracked down Leon Styles, meaning that Sam wouldn't be able to leap out, but that look had only lasted a split second before it had been replaced with fervent hope and belief in Al. This time, the expression did not shift. And it had been longer than a few seconds, now.

"He meant it," the Doctor said slowly. "He'd never…. This is all…." His mouth kept moving, but his voice was inaudible.

"Dr. Smith?" Gooshie asked, looking from the man's bloodless face to his white knuckles where he clutched one of Ziggy's terminals and wondering if he'd topple if he let go.

"Sam changed my timeline," the Doctor stated hollowly. He wasn't looking at Gooshie anymore; he was staring down at his hands, but Gooshie would hazard a guess that he wasn't seeing them.

"Dr. Beckett leaps in to change things, as you've discovered," Gooshie told him simply, not quite sure why the Doctor was reacting the way he was. "He shifts something in the past, putting it right. That's how he leaps."

"Oh, you know that's not true. You learned that when Sam leaped into Al. He would have leaped out even if he didn't fix the past. Even if all he did was make it worse." He shifted his gaze to Gooshie. "That's how Alia believed she leaped."

"We realized that, Dr. Smith," Gooshie acknowledged, wondering if he should alert Al to the Doctor's sudden mood shift, "but surely you can also concede that Dr. Beckett always changes timelines when he leaps?"

"Not like this," the Doctor replied softly. "It's different this time. I know how my past unfolded, and he—the other Doctor, the one I would have become, the one you met before—he knows how his unfolded, and Sam's changed that. He's interfered."

"Dr. Beckett's leaping is defined by his interference," countered Gooshie, trying to quell his nervousness. He wasn't sure he could win the argument, but he was afraid of what would happen if he lost it. He didn't know much about the Doctor, really. He hadn't completed his review of Dr. Beckett's leap in which he had encountered the Doctor before the Doctor himself had blocked the files. And his conversations with the Doctor hadn't made any more sense last time than they did now. Still, he had learned enough to know that if a smidgen of what the Doctor said was true, they were in deeper trouble than they had ever been in before. And that was saying something.

"Some events can roll over," the Doctor stated slowly. "Some events don't really matter in the long run and can be lost without causing any damage. Some new events are created. That happens whenever Sam interferes. Sam's not at a fixed point now, but he's in dangerous waters. With me being a time traveller, it's like…." He closed his eyes, pinching the bridge of his nose for a moment. Opening his eyes again, he said, "If Sam had never gotten funding for the Project, if he'd never gotten support, none of this would be here. And none of his changes would stand. You would have been stuck before you'd started." The Doctor paused. Gooshie, who recognized the look on the Doctor's face well enough to know that he was going to continue, refrained from saying anything.

"Well, no," the Doctor amended, beginning again, "I'd say it's more like when you lot nearly lost funding, once Sam was leaping about in time. You ran the risk of leaving him stranded, all because you would have been shut down, and no amount of protesting would have made them change that decision without evidence that what you claimed to be doing was actually being done. And you couldn't provide that evidence. But Sam changed something, like he was supposed to, and the effects rippled outwards, so your funding wasn't cut off. He saved the Project, and he saved himself.

"Now, say for a minute that something changed. Say that Sam didn't manage to do what he was supposed to, or rather that it didn't have the same ripple effect, or perhaps that someone else changed something somewhere along the line, and the Project did lose its funding. All of Sam's changes since then wouldn't stand. But let's just say, for a hypothetical moment, that the future Sam, who would have continued leaping when the Project still obtained its funding, in the modified original history, came back and realized what was happening. Realized that the history where the Project received its funding has been altered. Because something changed, he would no longer exist. Not once the effects took hold." The Doctor stopped for a few moments, then added, painfully, "That's what's happening to me. To him. And he…he knows it. He knows that he's splintering."

The Doctor turned away, sighing and letting himself slump against Ziggy for support. Gooshie stared at him, frozen, horrified by everything he was implying, as he added, "And I can't do anything to stop it."

A/N: As for the list of the Doctor's companions, I listed them as they occurred to me, skipped a few that I knew of and added a couple others I've only heard of but haven't actually seen in an episode (slowly working my way through it, though….), and I tried to get one from each regeneration. There were only the three deliberate ones that I felt would stand out from the rest, just on a slightly different level of the same plane, if that makes any sense at all. But, aside from that, they weren't in any particular order, either.

On another note, many thanks to anyone who takes the time to review. I have to admit that I am curious—had anyone gotten far enough inside my head to see this coming?