"What do you make of this?" Sam asked, gesturing to the console screen.

Martha looked at it and shrugged. "Nothing," she admitted. "I mean, the TARDIS never translates that. And that other bit, the part that's not writing…." She looked back up at him. "It's just a web of lines."

"Yes, I've been thinking about that," Sam said. "I think it's a portion of this time stream, featuring the major strands. See, look at this one." He pointed to one line in the centre. "If you follow it backwards, there were two lines. They formed one. And that one," he continued, pointing to one off to the side, "does the opposite. It diverges. That's what happened to the timeline we were following. What we need to do is cause it to converge, like that first one, since we can't go back to the point of origin to stop the divergence. That decision has to stand."

"What was that decision?" Martha asked, rather relieved that Sam had actually explained something to her instead of babbling an explanation at her.

"I don't know," Sam admitted. "I don't know if that's important." He frowned for a moment. Leaning back against the console, arms crossed, he said, "Tell me about your travels with the Doctor."

Martha stared at him. "You don't…remember, then?"

"Not that, no. Would've remembered you if that were the case, wouldn't I?"

"Point taken." She smiled at him. "It's brilliant, and I love it. Even if you can get us stuck somewhere. I mean, I met Shakespeare. There aren't a lot of people who can say that."

"Not sane ones," Sam agreed, laughing a bit. "But, even, look at this ship." He gestured to the controls. "She's been around a while."

"Well, practice certainly hasn't improved your landing skills," Martha informed him, laughing herself. "This last one was definitely one of the rougher ones. And I don't buy your claims of turbulence."

"What?"

"Well, you have to admit, if you hadn't been hanging on, you would've been on the floor right next to me."

"Did you say turbulence?"

"Yeah," Martha affirmed slowly, wondering what was going on.

"But wouldn't that only apply to space travel within the atmosphere? Were you in 1983 before this?"

"No. 1969. Long enough that I'm surprised you don't remember that, even if you are…whoever you are. Not entirely the Doctor."

"How does she travel? The TARDIS?"

"Well, it's not like you've sat me down and given me a lengthy explanation," Martha reminded him, "but we go through the Time Vortex."

"What is that, exactly?"

"I don't know. It's just…the Vortex. That's all you ever say."

"If I assume that it's the time web," Sam muttered, seemingly more to himself than to her, "then there can't…." He looked up at her. "There can't be turbulence."

"Well, that's what you said."

"But turbulence would suggest that something's changing."

"And doesn't that happen all the time?"

"From one perspective, yes, but from another, no." Seeing her look, Sam explained, "If you think of it as now, then, yes, everything's changing. It's your present; it would have to change, or you wouldn't get the sense that time's moving on. But if you reflect upon your past—"

"Then what's happened…has happened. Right?"

Sam grinned at her, the same grin the Doctor always wore, not the smiles Sam had been giving her before. "Oh yes," he answered enthusiastically. "Exactly. So for you to hit turbulence, you would have had to have passed a fluctuation. But if you were following one particular timeline, you shouldn't have; it should have been stable. The decisions would already have been made. Even in the greater web, each line would represent something that has already happened, for someone, at some point. For that to change, for you to hit turbulence, you must have crossed a fluctuation. And the only way for you to have passed a fluctuation would be if you crossed paths with another time traveller. Or yourself, at a different point in your own personal timeline. Understand?"

"Right. Sure." Martha nodded.

"And if you were—"

"No, wait," Martha cut in. "I don't."

Sam looked around, and then untied his tie, pulling it off from around his neck and holding it out, stretched between his hands. "Say this is one timeline."

"Okay. Right."

"And there're plenty of others all around it." He waited for her to nod before continuing, "At any particular point on the timeline, you can look back and see where that line has gone, as if you were reflecting on your past. You can't see the future, not yet, but if you take another point, and call that the present, then you'll see that it has followed a particular path."

"Okay."

"So, from start to finish, it's one line. But for you to have hit turbulence, someone would have to change the direction of that line. But the only way for that to happen—"

"Would be if someone or something is travelling in time," Martha finished. "Changing things."

"Exactly." Sam grinned the Doctor's grin at her again. But then the grin faded, and his shoulders slumped as he said, "It must have been me. You must have hit me. That's what pushed you onto this parallel. I caused this entire mess."

Martha smirked. "I doubt it's entirely you. I mean, look at the facts. You've been travelling for who knows how many years. And the Daleks have that temporal shift thing, which you said is how they got to Manhattan in the first place."

Sam gave her a confused look. "That's not what I mean. I don't travel the way you do. You or the Doctor."

"Okay," she agreed, "but, you know, I don't think that's exactly right. I mean, whether you remember it or not, you are the Doctor. Just a piece of him, that's all."

"I should have told you from the beginning." Sam sighed, the Doctor's face revealing ages of weary lines. "I just thought…. I mean, Al's always telling me…."

"Who's Al?" Martha interrupted.

"My friend," Sam answered honestly. "I'm not who you think I am. I'm not the Doctor."

"I know," she said. "You're Sam."

"And you're humouring me," he shot back. "Look, I still don't understand about this John Smith, exactly, but I'm not like him. He was part of the Doctor. I'm not."

"Of course you are," Martha corrected. "Or are you going to try to tell me that that entire speech on transdimensional ships was entirely yours?" She smiled. "I know it's confusing, but the Doctor— He's not buried easily. And he's coming out. Just like you did."

"Hear me out, please," Sam pleaded. "It's not like you think it is. My name is Dr. Sam Beckett. I'm a scientist. I devised Project Quantum Leap, an experiment that allowed me to travel through time within my own lifetime. I leap—from life to life, person to person. What you see is just the Doctor's physical aura. He's not here; he's back at Project Quantum Leap, in whatever year is their present. I rarely know where or when I am until my friend Al shows up, but he's only a hologram to me. He's tuned into my brainwaves, so that I can see and hear him, but no one else can. Usually. But the thing is, when you called me the Doctor earlier, and John…. I had to respond. That's what I do, every time. I take cues from whoever I'm with when I leap in until Al comes to fill me in, after visiting with the leapee—the person I've leaped into, I mean. There's a risk that I won't leap if people know who I really am, but sometimes, like now, I make exceptions, even if Al doesn't approve. Normally it would sound crazy, and sometimes it even sounds crazy to me, but surely that isn't any crazier than, well, this." He waved an arm around him at the TARDIS.

Martha was quiet for a moment. "That's, well…. That's quite the background story."

"No, no, it's not," Sam insisted. "Please, listen. I grew up in Elkridge, Indiana. I loved the farm, from the corn to the cattle. When I was younger, I wanted to be like my brother, Tom, and try for a basketball scholarship, but he convinced me to go to MIT. He recognized my potential. And since I've been leaping, I've realized how many lives touched mine, and how often I influenced that. The string theory of time travel—I'd conceived that with Professor LoNigro one summer, but when I was leaping, I realized that I also introduced that to myself when I was a child. I'd explained it to Moe Stein—Captain Galaxy—and I'd written him when I was young, asking about time travel, and he explained it on air as I'd explained it to him."

Martha stared at him.

"When I touch all those lives," Sam continued, "when I leap, I create one of those fluctuations you hit. I create turbulence in the Time Vortex, which you and the Doctor hit, throwing you off course. But something must have gone wrong when that happened, because I leaped into the Doctor, and I wouldn't have leaped into him if I couldn't fix something that had gone wrong."

"It is detailed," Martha admitted doubtfully, referring to Sam's tale. "But, if this is for real, then how do you explain knowing some things only the Doctor would know? Like the gate you were going to take me to?"

"Sometimes I pick up aspects of personality or tiny bits of knowledge from the leapee," Sam explained. "Think of it as leaving behind some mesons and neurons during the leap. I access those, usually unintentionally, to give me a better idea of my host. But if I concentrate on them, well…. You saw what happens when it works."

"But…." Martha looked far less certain of herself now than she had a few minutes before. "But…if you're not the Doctor, then…." She shook her head. "What am I supposed to do? I mean, I could be stranded here. I'd never see Mum or Dad or Leo or Tish or—"

"No, no, don't worry," Sam cut in hurriedly. "If anything ever does happen to the Doctor, Emergency Programme One will be activated."

"What's that, then? And why hasn't it been?"

"I…." Sam stopped. "I…don't know what it is, exactly. Just that it means you'll get home. But it's not been activated because the Doctor's safe, and so are you."

"And because of that, I'm supposed to trust you?"

"You trusted me before," Sam reminded her gently. "Even when you knew I wasn't the Doctor."

Martha shook her head. "No, I knew you weren't the Doctor, but I thought it was still him, buried underneath. And now you just told me it was all a lie." She offered him half a smile. "Though I guess because you're telling me everything now, I have to give you some credit." She was silent for a moment. Then, "If you have to fix something to leap, and the Doctor won't come back until you do, then we'd better find out why you're here, shouldn't we?"

"That's what I was talking about earlier," Sam told her. "I've been studying the diagrams on the console for a while now, and I've been thinking about what you said. You hit turbulence and ended up on this parallel, Martha. And the thing with parallels is, you can't tell which one you're on, because they're so very nearly identical—at least until they're mature and separate completely into a parallel world, whereupon the accumulative changes would be noticeable. I think…I think I caused that turbulence. I think you would have been safe on the other parallel otherwise. And without the Doctor on this parallel, there probably wouldn't be an anomaly that would force the necessity to splice the parallels together. Which means when you landed here in the original history, you landed on the other parallel."

"Wait, hold on," Martha stared at Sam. "What do you mean, original history? According to what you were saying earlier, with straight lines, with your tie—" She stopped. "Oh. So this is another fluctuation, then, that would create turbulence." She swallowed. "Let me get this straight. You said you change things when you leap, yeah?" Sam nodded. "So what's happening to me, now, has already happened for you? Only, because you're here now, and you're changing things, you're rewriting history. Changing my timeline a bit, because you're you and not the Doctor. And the original history is what happened for you, but what's happening for me, now, is the…revised history."

"You, Martha Jones," Sam proclaimed, "are positively brilliant." He beamed at her, the Doctor's grand grin of approval, and she had to remind himself that he really wasn't the Doctor, no matter how much he looked like him. "But, because you hit that turbulence, you landed on this parallel instead. Only, you weren't supposed to, and now that you have, the Doctor has to splice the parallels together instead of cutting them apart. Only he can't do that by himself, I don't think. Which is why he needs me. That's why I'm here, I think. To help him."

"Wait. Just…wait." Martha held up her hands. "Why do these parallels matter so much?"

"Because this one isn't viable. Something's gone wrong, and it's going to end."

"What?" She stared at him. "This parallel is going to end?" Sam nodded. "But…how is the Doctor supposed to fix this when he's not even here? I mean, if he's back in—sorry, when did you say you were from, again?"

"I believe that my relative present is currently anchored in 1999. At least, I think that's what I heard last, and I expect Al will let me know when we reach the millennium. He won't be able to resist telling me about the night he had, ringing in the new millennium." Sam stopped. "Unless he has told me already, and I've just forgotten."

"Okay. Right." Martha shook her head. "Look, no offense, but even with 1999's cutting edge technology, the Doctor won't be able to fix this mess from there. Well, maybe, but…. I mean, sure he's inventive and clever and all, but how quickly do you think he could fix things when he has to scavenge and cobble together some piece of technology to do this? If he needs to fix this, you're not helping matters by leaping into him and trapping him there, away from the TARDIS." She was silent for a moment. "You can leap into anyone, right?" Sam nodded, so she continued, "So if you leaped in just to help the Doctor, then it would've made more sense for you to leap into me, wouldn't it? I mean, you'd probably be more help to him than me. I'm studying medicine, not the science behind time travel."

"I asked the same question."

"And?"

"I don't think I know the real answer yet." That was true, as far as Sam was concerned. He didn't believe the Doctor's simple claim of experience, and he didn't want to think that he had leaped in here for a reason other than to help the Doctor. Because if he was the cause of the turbulence that had shunted them onto this parallel—for surely the Doctor would be watching out for the disturbances he had caused—then the Doctor's predicament was entirely his fault. And he knew he hadn't imagined the fear or pain he'd seen on the Doctor's face as he spoke of splintering.

Al saw Dr. Verbena Beeks heading towards him and sighed. With his luck, she wouldn't leave him alone. Actually, he'd been expecting her to corner him earlier. He kept chalking up his escapes to good luck. Now, he was caught out in the open. But if he couldn't avoid the attack, he could at least lessen its ferocity. And he was fairly sure Beeks wouldn't say as much as she wanted in front of anyone else, so all he had to do was get to the Control Room.

"Admiral," Beeks called, increasing her pace to catch up with him. "Al, hold up a minute."

Pretending he didn't hear her, he turned into the Control Room. Excellent. Both Gooshie and the Doctor were there. Beeks certainly wouldn't try to give him the third degree with their leapee there. "How's it going?" Al asked, not sure he liked the look on Gooshie's face, let alone the Doctor's.

"Al," Beeks began, coming into the room. She stopped short at the sight of the Doctor. "Admiral," she corrected. "May I have a word?"

"Once I'm finished here," Al reluctantly agreed, planning to drag it out as long as possible and then try avoiding her again. Beeks's lips tightened, meaning she was on to him, but she nodded, so Al continued, "Ziggy, can you locate Sam?"

"Negative, Admiral."

"So much for keeping in touch," Al muttered. "Gooshie, what have you found out?"

"I…. That is, it appears, Admiral, that…." Gooshie kept trailing off, unsure of how to answer the question. "Dr. Smith has…. Dr. Beckett may not be our immediate concern."

"What?" Al looked from Gooshie to the Doctor to Ziggy and back again. "What do you mean?"

"As I understand it, Admiral, Dr. Smith is…splintering."

"Splintering?" Al repeated. "What the hell is splintering?"

"Exactly what it sounds like," the Doctor responded grimly. "And he means the other me, not this me." He straightened up, his face unreadable. "When Sam leaped into me, he didn't just land in a pocket on another parallel. He changed my timeline. That can't be undone." He leaned back against Ziggy, closing his eyes. "When you get in contact with Sam, Al," he said, not bothering to open them again, "take me into the Imaging Chamber with you. I need to talk to him. Well, through you, unless I have enough time to do some more fiddling. And I need you to tell me what you see if I don't, because I need to know what they've done. Well, providing I can tweak things here and get you a signal in the TARDIS, at least temporarily." Leaning forward and opening his eyes, he continued, "Because I'm not sure exactly how long I'll be around to help Sam out."

"You're not telling me that you think Sam leaped into you to change your timeline just by bringing you to the Project early," Al stated incredulously. "Are you?"

"No. Well, I hope not." The Doctor sighed. "I'd rather like to find out what my other self thinks. What he's found out."

"Ziggy," Beeks asked slowly, "would it be possible for you to sync the Doctor's brainwaves with Sam's?"

Al blinked, surprised. She'd been talking to the Doctor already. But he knew how much the Doctor tended to say—slim to nil, no matter how much he rambled on. Just enough to confuse her and stir up her curiosity, even if she did ask the right questions. So Beeks couldn't know much. Which meant that she probably wanted to talk to him about the Doctor rather than about Sam or his relationship with Tina or the fact that he should talk about his concerns and not bury them, yadda yadda yadda. And the fact that he hadn't enlightened her on the Doctor's last visit. He'd spent a month burying the truth behind all sorts of red tape, and he didn't fancy sifting through all that paperwork. The conversation wouldn't be a pleasant one, no matter how much Beeks would try to make it so.

"Negative, Dr. Beeks," came Ziggy's smooth reply.

"I suppose that would be too easy," Beeks agreed reluctantly. "If we could do that with just anyone, we'd have no trouble giving the officials their proof." She allowed her displeasure to show for a moment before carefully schooling her features again. "Doctor," she asked, addressing their leapee, "was I right in my interpretation of you as a scientist?"

"Well…sort of." The Doctor offered her a weak grin. "I have lots of experience in this field, actually." He waved a hand around him. "Plenty. This is all a bit...elementary, really, if I'm honest. And I like to be honest. So to answer your next question, yes. I am a time traveller. And that's the heart of our trouble. Well, my trouble. Only your trouble if we can't splice together those parallels in time."

"Whaddaya mean, splice together those parallels?" Al asked, wishing the Doctor would just say things straight for once. "Sam didn't say anything about that."

"No, I don't expect he'd want to tell you, if he knew," the Doctor replied, looking off into space somewhere over Al's shoulder, eyes fixed on a rare blank space of wall next to the doorway. "I didn't even want to tell you. But I'm not sure that it matters, now. You see, I don't know what I've done. I mean, what I'm going to do. But I can bet that, somewhere along the line, I've saved the earth. But now that's all becoming undone. I can't guarantee that I'll make the same decisions now. I'd like to think I'll try." He looked back at Al now. "But I have to watch, and I have to see how things unravel. If they do. I need to watch the ripple, track the cracks. Count them. I'm going to try to patch them, but—" here he waved a hand down at himself "—I'm not exactly fully equipped to do that. I can only do what I can in the here and now. No fixing at the source. Which means that it will keep spreading, weakening. And there're only so many times you can patch something before it changes, just a bit."

"I think that you had better enlighten us on these parallels, Doctor," Al growled. "The Type LXXVI one or whatever you keep going on about."

"A Type LXXVI parallel isn't long-lived," the Doctor said, shifting his gaze over Al's shoulder again instead of looking any of them in the eye. "Something's gone wrong, and it will terminate. Plenty of types of parallel termination, and it doesn't matter which kind, usually. I mean, normally, I can let it end. Other times, I can just cut it off, let it form a parallel world prematurely. Doesn't usually cause any harm, and if it does, it's not hard to fix. But the parallel world wouldn't be viable, and it would disintegrate into the Void, so to speak. But sometimes, there's something that you need from the original timeline, and you can't just cut it off, because you can't risk losing that. That's when you have to splice the parallels back together. And they have to be the right parallels or it won't last long. Grafting's rarely an option, you see; hardly ever works, even as a nurse graft while you get your affairs in order.

"But, pinpointing those parallels isn't as easy as you'd think. Every second, there are thousands of parallels being created. Millions. Every decision, another parallel. Another path. And they aren't isolated, oh, no. They crisscross each other. Interlocking decisions. Some converge with one another and remain that way, and some converge in some areas and diverge in others. But just because a parallel exists doesn't mean a parallel world will form. It doesn't, usually, though that's not to say that there aren't billions upon billions of parallel worlds out there. And it doesn't mean that that parallel wouldn't have been viable, just that the decision, in the long run, really wasn't important. That parallel will always converge with the initial timeline again, none the worse for the wear. Essentially, all that happens there is the timeline shifting around the decision, otherwise unchanged."

"Doctor, get to the point," Al ordered, his voice low. "What happens if that parallel isn't spliced in time?"

"A Type LXXVI parallel termination is absolute," the Doctor answered softly, shifting his gaze to look at Al. "Anything on it will be lost." He looked back at the doorway. "And I'm sorry. I am so, so sorry. But that will include Sam."

Al heard a choked sob, and he turned to see Donna. She sagged in the doorway, the first tears that escaped trapping a stray dark lock of hair against her cheek. The Doctor hadn't been talking to the wall. He'd been talking to her the entire time. Telling her, in no uncertain words, that her husband was going to die, and she wouldn't be able to do so much as bury his body, let alone see him alive one last time.

Al felt the anger rise in his chest. The Doctor had no right to break her heart, not in that way, not right then, not without definite proof. They hadn't even run any scenarios by Ziggy. He couldn't know, not for certain. He'd said it wasn't fixed. If it wasn't fixed, it was in flux. And if it was in flux, it could be changed. The Doctor had told him that last time, more or less, and Al had been around Sam long enough to vaguely follow what the Doctor had been saying, then.

Verbena moved to comfort Donna. She didn't say anything; she just wrapped her arms around her and let her colleague, her friend, cry. Al knew her well enough to know that she'd shed her own tears later. He respected her for that. Verbena Beeks was a strong woman, and she could anchor Donna now that the Doctor had set her adrift.

"You can't know that," Al stated hollowly. "You can't know that that will happen."

"That's what will happen if the parallels aren't spliced," the Doctor rejoined bitterly.

"And what does that have to do with your splintering?" Al shot back, still not tearing his eyes from his friends.

"You wouldn't understand."

Now Al turned to look at the Doctor. "Try me."

"I've been simplifying my explanations as it is," the Doctor said, his voice still sombre, his eyes still sad, his expression still saying that he wished he could do something but he just couldn't. It was the same look Al had seen when he'd asked the Doctor to fix the retrieval system last time. He'd been refused that time, and he'd accepted it, but this time he wouldn't back down. He needed to know.

The Doctor must have recognized and accepted this, for he continued, "Think of it like this. There are more than a million, billion timelines out there. Some cross. Some don't. When I was saying timeline before, I didn't exactly mean a timeline. Well, I did, but it's broader than that. A timeline for this reality, not just a personal timeline. It's the timeline for this reality that's split into parallels. And these parallels are made up of, oh, so many threads—and so many strings in every thread. Personal timelines. They're personal timelines. All intertwined, woven together to create the larger timeline. Some touch each other. Some don't. They end and they begin, but the fabric they form is never broken. Right now, that fabric is more like a square on a patchwork quilt. It encompasses so much, but it's part of something larger. But that quilt, it has a flipside. A mirror image. It's reversible. Except…sometimes it's not, in certain places. It can't be; it's all cobbled together, bits and pieces of times and realities. But sometimes, if there's a loose thread, and you pull it out…." The Doctor sighed. "You can unravel more than you intend."

"So what's splintering, exactly?" Al demanded, raising his voice. "Snapping that thread?"

"To keep to the same analogy, yes. To a point. Yanking that thread out, snapping it, weakens the overall timeline. You snap that thread, and it frays, snarling other timelines, other events. You can't do it without affecting something else. Another life, perhaps. Maggie Dawson for Tom Beckett, for instance." The Doctor stopped. When Al opened his mouth to retaliate, he added, "Only with me, it'll be worse. Because I have touched so many lives, Rear Admiral Albert Calavicci. More than you can imagine. I don't know how many more I'll touch between now and then, but I reckon it's a fair bit, and removing that thread from the pattern will be like taking apart a seam. Not just one seam, all in a line. There'll be holes over the entire quilt, because I don't stay in one time, on one world. I travel. So it'll be messy."

Al glared at the Doctor, and the room was silent for a few moments, save for the electronic hum in the background. To Al's surprise, Gooshie broke the suffocating silence. "Then…then we'll have to ensure that the parallels are spliced," he declared, albeit shakily and with less confidence than Al would have hoped. Even so, he had to credit him for trying to take charge. Although that was his job, not Gooshie's. Still, Verbena's calm, assertive presence was dealing with Donna, and if he was honest with himself, he wasn't sure he could have spoken right then without snapping at the Doctor.

A small smile twitched at the corners of the Doctor's mouth, but then he seemed to remember something, and it died. "Precisely what I'd say," he announced, with more gusto than he ought to, Al thought, looking as he did. "Let's get to it, shall we?" He offered them a grin, but it didn't reach his eyes, and Al knew it was all a show.

Still, he couldn't say something, not now. Not in front of Gooshie, who was trying so hard to remain optimistic. He was chattering away to Ziggy now, doing what he could, doing what he knew best. Al looked across to Donna and Verbena. The latter caught his eye, mouthing that she'd speak with him later. He nodded in return. Donna was drying her tears, clinging to the Doctor's latest words like a lifeline to pull her back to shore. Al couldn't cut it, couldn't throw her back out to sea by pointing out that the Doctor wasn't telling them something. The Doctor wasn't easy to read, and Al found it difficult even now, but he knew one thing with absolute clarity.

The Doctor was keeping his silence in an attempt to protect them, to spare them. He'd known what his words were doing to Donna as he'd said them, but he hadn't curtailed them, not then, because they'd needed to be said. But he'd made the choice not to tell them everything. He hadn't mentioned the pocket. He'd only said a bit about the parallels. He hadn't elaborated much on the splintering, either. He'd given them some information, but not all of it, and Al could only hope that it was enough, as the Doctor had obviously judged it to be. The time would come when he'd have to finish his speech. Al wouldn't even have to force him to do it. He'd have to tell them, all of them, whatever he had left out.

Al could only hope that it wasn't something that would forever tear apart the family they'd become at the Project.

A/N: So, hopefully the explanations weren't terribly tedious, and hopefully some of them make sense, or at least partially make sense. But, I tried to throw up enough questions to keep you all interested and guessing. It's much more fun that way. Thanks to those who review—I certainly appreciate it!