As it turns out, Lizzie does know what a car is, and what it does, and how to make it go and how to fix it when it won't. She also knows what a stoplight is. She knows what bagels are. When she concentrates, she finds that the word 'barista' is already in her mind. In fact everything here, while strange and new and utterly shocking for those first moments, is familiar when she takes just a second to reflect. It's not even very deeply buried. Hardly buried at all. Like there are a thousand little drawers in her head, little pockets of information, and she always knows just which one to open.

It's the same as walking in the woods and seeing a new flower; she just knows.

"Doctor, this is very strange."

Gently, understanding, "Overwhelming for you, I imagine."

Lizzie shakes her head. The girl Jessica has taken off, and is halfway down the street buying a hotdog from a sidewalk cart, probably full of salmonella. Salmonella. When Lizzie thinks of street food and disease, she knows what salmonella is. "Just the opposite. It all feels so natural."

"It's exactly what you've always done. What you called your witchcraft. You never had any reason to know it went any deeper than that."

"And how deep does it go?"

But he's looking over her shoulder and nods, "I think Jessica's asking how you want your hotdog."

Just a thought, and the flavour of the overcooked meat is on her tongue, and the flavours of the various condiments come and go until they form their most pleasing combination. "No mustard," she mumbles, and sees the instructions relayed by hand signals, "and extra onions. Doctor, what is this?"

His smile is electric, gleeful, as though he has the pleasure of explaining Santa Claus to a toddler for the first time. "Knowledge!" His big bony hands make more shapes in the air. These ones are meaningless, except to express the wild unbridled excitement he feels, so potent those hands can feel it physically and would capture it. "Lots and lots of it. Encyclopaedic and sensory and fully experiential and instantly accessible! Like the internet, except without the bad bits and the audience participation!"

'Internet' is quite a large concept. It takes her an extra beat to comprehend that. Gives him time enough to add, "If it helps at all, I'm madly jealous."

Jessica returns, balancing two hotdogs in one hand while pushing a third into her own mouth. Still she has an elbow free to stick in the Doctor's ribs. "Not does. Jellyus am being bad thing."

"So's talking with your mouth full. Now, remind me later on, when we've got a minute, that I want you to sit down somewhere quiet with Elizabeth and tell her your full name. It's an experiment, and it's important."

"Why not does now?"

"Because what neither of you, not the super-intelligent one nor the highly-trained former intelligence operative, seems to have noticed is that just down that street opposite, there's a huge crowd and a number of ambulances and police and fire engines and allsorts."

They turn, both in sync, to look where he's showing. Glance at each other, confirming it. There is, yes, a huge crowd just down the next street. Either of the ladies, if asked, would add that it has crowded around a large pit which has collapsed inward, swallowing the whole intersection.

Lizzie, once she's had a look at the street signs, would add more. She'd say that in 2086, Earth's America embarked on a program to expand its subterranean public transport system in an effort to make transcontinental travel easier and more affordable. After the fall of oil as the primary means of power, deposits mined out of parts of the United States had become the new source, leaving the superpower self-sufficient, other countries dependant and willing to pay. This vast and rapid expansion had led to several similar collapses and disasters.

Virginia's, in 2086 (September, for those who care for details like the ones Lizzie now has), was notable only in that there were no casualties.

And for what was found at the bottom of the pit.

"Adam," she says. "They're going to name him Adam."

"Names who, Lizzie-Witchperson?"

The Doctor tries to take his vengeance for her earlier violence. He, however, is much taller, and try as he might can't angle his elbow into her ribs without lowering himself almost to his knees. "Stop fishing for spoilers. It's only down the street, you can wait and see."

Jessica becomes suddenly very motivated. The crowd might otherwise have proved an all-but-impenetrable barrier. But where Jessica moves amongst them they jump away, clearing a channel as though pricked with tiny needles. Lizzie and the Doctor need only fall into her wake, until the police cordon looms. Then, the Doctor pulls her back. "Don't talk," he says, "and keep your arms covered. Lizzie, difficult as it might be for you, pretend you know nothing."

Then he quite simply reaches for the crime-scene tape and lifts it like a gentleman, allowing them to duck through. By the time the Doctor himself is managing the tricky feat of manoeuvring his own spindly limbs beneath the ribbon, the nearest officer has arrived to shoo them away. "Ah! Good afternoon, Inspector!" Somehow, the Doctor's knee is turned once through the tape, and his shoulder has not quite made it under yet. "No, wait, America, not Inspector, it's… Detective? Good afternoon. We're from – Jessica, get the paper out of my jacket, would you?" The girl rushes up and feels around his inside pockets. Lizzie watches her come out with a little folded cover, and inside nothing but some plain white paper. She places this into the one of the Doctor's hands that might nominally be described as free. "We're from, the… uh… um… Jessica, you do it. Remember to concentrate, which I can't."

The girl takes the cover back, and shows the paper to the baffled detective. "Them am-" she begins, then with incredible force-of-will corrects herself, "We are most totally supposed to be being here." So perfectly earnest is she that Lizzie almost believes the detective takes her word for it. But the paper holds his eyes. After seeing it, he is so silently, determinedly helpful that the Doctor (once he has extricated himself from that flimsy plastic barrier) looks at his seemingly innocent little friend with impressed and almost fearful awe.

Behind the detectives back, he hisses, "You're getting terribly good at that."

"But was to have been being truth-tells. Are being supposed to be here. Tardis am having said so."

Psychic paper. The detective believed because Jessica believed. In whatever vast stores of information Lizzie has access to, 'psychic paper' moves from being an unconfirmed rumour to being a genuine artefact, of one known and verified occurrence, in the possession of the Doctor.

Then, finally, they are brought to the edge of the collapse. The asphalt has fallen away in huge slabs, lining the sides of the pit like giant scales. At the bottom, a fire crew has just finished work, clearing a space. And there amongst the rubble, the neon glow of hi-vis jackets, a team of baffled paramedics trying to work, and not quite knowing what to do with themselves.

"He's comatose," one is crying, as though it's the simplest thing in the world and the rest are ignoring it.

But the lady who holds the full-body scanner shakes her head, taps the screen with the back of her hand. "Nate, look at the readings, would you? Look at the brain activity. There is nothing wrong with him."

A second man, the last of them, yelps and steps away from the body being discussed. "Damn it, he blinked. The hell is this?"

Jessica ducks behind the Doctor and pushes him forward. While he reels on the edge, "I couldn't agree more, but I'll do it in my own time."

She groans and goes ahead of him, hopping from stone to stone, finding the most stable route down. Faced with two possible steps, she hesitates, and leans towards the left. "Wait," Lizzie cries. Physics, the way the other rocks are lined up against each other, she'll start a slide. Injure herself, cut off the emergency workers at the bottom, strand both witch and Doctor halfway down. "The other way," and though the asphalt scale wobbles, though a scattering of gravel falls away from it, there is no such catastrophe that comes to pass.

At the bottom, Jessica waits. She's been noticed, but then she was told not to speak. Told to keep her arms covered too, so she won't lift them even to wave hello. Stands blithely smiling, gesturing to the approaching Doctor – he'll explain everything.

The medics, for lack of anything more productive to do, accept this, and watch him coming. It's that or argue about the body-scan again.

The Doctor, as a matter of fact, explains nothing. He flashes the psychic paper with barely a thought and moves them out of his way. He could make something up if he really wanted to but really? Honestly? Lying's no fun. It's the things you have to lie for that are fun.

In this case, it's a man. He looks like a perfectly normal man. For 2086, his clothes are a little out of date. Straight-cut jeans, a checked shirt, a padded bodywarmer over the top. He looks almost familiar, this man in the pit, except that his hair is dark, and his eyes are green. They are also wide open and, as the third medic was so shocked to discover, they occasionally blink.

Which is nothing so odd, the Doctor muses. All eyes blink. It's how they keep moist and focussed and clean. Blinking's a very useful thing indeed. But usually, someone who is able to blink is able to do other things as well. Like move. Talk. Sit up. Dance the rhumba. Generally they don't just lie at the bottoms of deep craters, flat on their backs, arms straight by their sides, staring at the sky. And blinking. Generally they do a bit more.

He looks up from this mystery and into the three baffled faces. Not a one of them has even opened their mouths yet. Gesturing to the man on the ground, "Um… story, maybe?"

"There's no story," says the one called Nate. "They were drilling the tunnel and there was a cave-in. And when they started clearing the debris, there he was."

"He hardly looks like a quarryman," Lizzie cuts in. She is looking, in particular, at his flat canvas trainers. How lucky he is to live in a time when marking one's clothing with a five pointed star is not a death sentence.

"Well, that's the big question," says the woman with the scanner, "He's not one of the tunnel crew, and the police already looked at the footage from a watch-drone that was in the area; he wasn't here before the collapse."

"Then he was underground already," the Doctor says. "The cave-in only revealed him."

The woman scoffs, "You really think that's likely."

"No, not at all. Not in the slightest. But it's definitely possible, in a vague, outlandish sort of a way, and it's the only other explanation. There's probably a very neat, eloquent way to condense that sentence, but it's for a much more thoughtful man than I to do the condensing. I'll never need to bother with that sentiment again, so I shan't bother rephrasing it. Anyway, never mind how he came to be here. That's not what you were arguing about. You were arguing about his condition, tell me about that."

He was addressing the ambulance crew.

It's Lizzie who answers him. On her knees, next to the still-breathing man with his still-regular heartbeat and his blinking, she says quite simply, "Empty. There's no person here, Doctor. There's a human. Living and breathing. But there's no person."

Jessica, having happily devoured her own hotdog, comes now and takes the remaining half of the Doctor's from his hand. Almost before he has noticed the theft, she has replaced its weight with something she found while they were talking.

The man, the one Lizzie says they will name Adam, had a bag with him. In the rush to help, it was thrown or kicked away from the body. Jessica has been rooting through it these few minutes. What she has just given the Doctor is a newspaper. He glances at it and then slowly turns to look at her. "While I'm sure this devastating hurricane really was a tragedy of untold proportions, I'm not entirely sure it's got anything to do with-"

She rolls her eyes, "Is to be looking at numbers of date, please."

The Doctor looks again. "Oh," he says. "Oh. Quite a large 'oh', actually. November twentieth," it says.

"But it's only September," says the skittish third medic.

The Doctor hands him the newspaper, fresh and white as the day it was printed, so that he may see for himself. Says darkly, "2013."