The crack seals behind him and he settles down to wait. He and the TARDIS here at the beginning of all things -- he rather likes it, to be honest. He's been with the TARDIS at the end of all things so often it's become cliche. Technically speaking, since he's outside time and space, he supposes that he's here at the end of all things too, but it's never, this is the important part, going to be his fault again, and he thinks he rather enjoys that as well.
"Why are you talking to yourself?"
Well! He props his feet up on the console. The hallucinations starting a bit earlier than he'd expected, but auditory is perfectly acceptable, that's normal, even classy -- it's visual that he has trouble with.
"Well, let me give you some visual, numbnuts," says the child's voice again, and there are distinctly two sets of footsteps before he hurriedly squints his eyes shut. "...Wow. Really?"
"I can pretend I'm not going madder if I want to," the Doctor informs his hallucination. "I can do anything I like. I'm not in the universe."
The child sighs. "Open your fucking eyes, okay? You are the worst end boss in the history of time. And I know something about the history of time."
End boss? The Doctor opens his eyes and sees: an American thirteen-year-old, his timeliness so looped and knotted around himself they're almost painful, a walking paradox in a frankly snazzy suit. He's accompanied by a girl tangled in the same web as him, and now that the Doctor isn't closing his eyes and pretending none of this is happening, he realizes that there's another pair outside -- he activates the camera and it delivers him a series of Polaroids that show paradox twins with goofy looks of wonder on their faces. He flashes one to the boy. "Are these your friends?"
In answer, the girl outside yells, "Dave! Rose! You are totally not going into the end cave by yourself!!!"
"Seriously," the boy adds, beating on the TARDIS doors, and the Doctor obligingly opens them. "I don't care how many cheat codes you-- oh man."
"Right, bigger on the inside than the outside, got that part," the Doctor says, keeping his eye on the child with the bowtie, who is clearly the mastermind of this operation. "Not a lot of time to talk. In fact strictly speaking no time to talk. You shouldn't exist."
"Dave," says Rose, presumably. "The gods--"
"Lord English, right?" Dave says. "I mean, come on, you're in suspenders, you've got a magic time machine, you came through the Rift. If this isn't Lord English, I'm kinda disappointed with the universe. It is fucking up on the coincidences."
"You shouldn't exist," the Doctor says, "unless your whole universe was eaten by the crack," and he leaps up onto the console, licking one finger and smelling the air. Below him the human with the black hair sighs happily. "Don't touch that. Your whole world was pulled through. But you're from Earth."
"Man, if I had a nickel for every time someone told that to me, I'd be like ghost Bill Gates here and John would have to shoot me with Bill Murray's ray gun," Dave complains. "Can you just stop being like a kooky old dude and hold still so we can beat you?"
"It's a classic gambit, the video game construct, the end of the world scenario, except for that the world never ended, in fact it's still going right now, without us, so how can you be? You don't have a time machine." He glances down at the ... record ... things that Dave's hands rest on and says, contemptuously, "Wellll, not one that's any good. You were not at the eye of a storm. You should be entirely erased. And when you were entirely erased, your game went too, and this Lord English never came because he was never allowed in in the first place." He beams delightedly at them. "You're paradoxes without a planet, and I hope, I very much hope, I in fact firmly believe that I am about to both give you back a planet, and," he says, leaping back down, "a wedding."
"But, sir, we've only just met," says Rose, with devastating deadpan, and he bends down to make sure it isn't Romana in tiny, purple-dressed disguise. It isn't, but her paradox gives him a headache, so he withdraws. "And your uncanny habits might put a damper on the wedding night."
"You're going to get us back to earth?" says the black-haired girl, the only one of these children who seems remotely willing to act her age. He likes her immediately. "Did you guys hear that?"
"It depends," he says. "It depends intensely on one small, seven-year-old child."
"Okay," says John, holding up both hands for everyone to be quiet. "Guys. This makes no sense at all in any way."
"I know," the Doctor says. "Isn't it exciting?"