Chris was often mocked for the interests that she had. They were not, people said, the ones that a girl should have. Olympic records and dinosaurs, the hardest to find fizzy drinks. The Egyptian afterlife for a while, until her teacher had complained. But one thing Chris had in common with most eleven-year-olds was that she was absolutely not interested in rocks.
"And another interesting thing about these rocks," the Doctor was saying from behind her astronaut's helmet, "is that I think they're emitting gravity somehow!" She threw one up above her head, where it hung in an improbable way. "And that's impossible, of course. And they're turning into oil, which is impossible in a completely different way—"
She turned round to Chris, her face falling.
"—and you're ignoring me and fiddling with your phone," she said.
"I'm playing my game," said Chris, disgruntled. The only spacesuit the Doctor had in her size was a novelty one – all black and white splotches in the manner of a cow – and being forced to wear it had put her in a very bad mood.
"You can play that anywhere! You're on an asteroid! Look how high you can jump!" said the Doctor, bouncing high in the air to demonstrate.
"I suppose," said Chris. "But I thought traveling with you would be lots of fun adventures. Not looking at rocks on an asteroid."
"Ah," said the Doctor with a smile. "But to the well-ordered mind, looking at rocks is the biggest adventure there is!"
"No it isn't." Chris looked down past the too-near horizon of the asteroid where they had landed, where the upper hemisphere of a planet took up the entire sky. It was like her own, all countries and seas, but in different shapes that stretched around the world. The sun was on the other side of it now, and cities spread their lamps across the night, marking out an alien civilisation that from this distance looked just like her own.
"It's beautiful," said Chris. "Much better than rocks."
"It's an astonishing thing, isn't it?" said the Doctor. "Seeing your planet from space for the first time."
"But that's not Earth!" said Chris. "We don't look anything like that! There's no Africa, and we all should live up there"—
"Well, everyone looks different when they're younger, don't they?" The Doctor shrugged. "Even planets."
"But there are cities down there! There's people, aliens! There weren't any people on Earth when it didn't have any of the countries!"
"And how," said the Doctor, "would you know about any of that?"
"Because we'd know! It'd be in the books!"
"Not if the books didn't know about it, either."
Chris frowned. "We would know. There'd be old cars and messed up teddies down by all of the dinosaurs. There would be something to tell us that people'd lived. There wouldn't be nothing at all."
"Thing is," said the Doctor, "you're used to seeing it like a book. Where everything's just knights and cavemen, and all of what happened before you lot gets a page to itself at the start. Makes you forget how much time there really was, scrunched up into that tiny page. How much space there is, for something to get forgotten."
"But there'd still be something," said Chris, insisting.
The Doctor didn't answer her, because she wasn't listening. She was looking at three figures in spacesuits, coming up from the asteroid's edge and walking towards them both. She knew exactly what they all were, and how that meant Chris was talking about exactly the wrong sort of thing.
"Hey, look, Chris!" she said. "It's people! Hello, people! Fancy bumping into you on an asteroid; it's a small world."
She grinned at her terrible joke, but the three figures didn't grin back. They had scaly faces and reptile skin, but their expressions were strangely human— and their eyes conveyed total contempt at the Doctor and her wave.
"Aliens!" one of the figures said. "Funny, isn't it? How they always look like us, but with animal heads."
"Staking a claim, are you?" said another with hostility. "It won't work, I'm afraid. This asteroid's Earth property, by every law that applies. And don't go saying laws don't apply to you, just because you're aliens. Our people've dealt with that sort of rubbish before."
"I'm not an—" Chris began to say.
"Annoying enough to make up phony laws," finished the Doctor as Chris glared. "Neither of us are! We're just here making a documentary. Called Planet Earth, and about it. And all the rocks that're passing it by. And we're doing this rock, now, 'cause there's been a whole lot of series. And we're running out of places we haven't been."
"I'm a human," said Chris, from"—
"Planet Hume," said the Doctor. "Which isn't a bad place, really. There's shops in most of the cities, although a lot of them keep closing down."
"Stop, Doctor," said Chris, getting annoyed. "You keep talking over me, and I always tell you to—"
"But I expect you're wondering who these people are, Chris! And that's a hard question to answer, as they have all sorts of names. Silurians, Homo Reptilia. But a more appropriate name for them right now"— she looked very meaningfully at Chris —"would be Earthlings."
"Oh," said Chris sadly. "From there."
"From there. Just like you're from—"
"Planet Hume," sighed Chris. "I'm from Planet Hume."
"We have permission, as well," said the Doctor. She fished a piece of paper from the pocket of her jeans, and handed it over to her apologetically.
"Huh," said the figure, after looking at it for a while. "I wouldn't have thought the Queen would allow this. Kala, Drocks! It's legit!" they said to their two curious colleagues, "they're not a threat after all. They're from Hume! A mammal planet, where everyone is furry!"
"Everyone isn't furry," said Chris.
"What would interest anyone about this place?" said the figure who must have been Drocks. "Yeah, there's the oil, but even scientists find that a bit dull. It hardly makes for an interesting piece of TV."
Chris sighed. "We really love rocks," she said miserably. "The aliens from Planet Hume. You have tellies?" she said, as an afterthought.
"Well, of course!" laughed the figure. "Earth's not some backwater, just because we've not got many spaceships yet."
"Well, we'll be coming with you, if that's alright," said the Doctor, "an asteroid full of oil, and nobody even knows why! They'll love that, on Hume TV. They've only one telly station," she added, "it's them who's very backward."
The closest figure sighed deeper than Chris thought a reptile could. "Okay," she said. "Come and film how very dark it is, or whatever. But don't interrupt our mission! And don't think you'll be getting Humans down to Earth as tourists! It's very hush hush that aliens exist at all. There's only a few of us who know."
"I don't think you'll have anything to worry about there," said the Doctor. "Hume is"— she wrinkled her nose —"it's so very far away."
"Do you miss it?" asked Drocks. "Bol here can't stand going abroad for a few weeks, and you must've come millions of miles."
"Oh, I'm not from Hume," said the Doctor. "I just look like I might be, if there's things you aren't able to see. But I like it a lot down there. They're good people."
"If you're sure," said Kala sceptically.
"Come on," said Drocks impatiently. "They haven't done anything wrong! They've just come here in that tiny box over there. They've nowhere to put anything they could steal."
"They could kill us," said Kala.
"They're not going to kill us," laughed Bol. "They're telling the truth, I think. They're just who they say they are, and nobody's going to die."
Not yet, Chris managed to stop herself from saying. She wasn't stupid, in the way people assumed an eleven-year-old would be. For her Earth to come into existence, the one the lizards were from would have to stop, disappear so completely that no one would believe it could ever been there. She had no idea if they'd even thought of what Earth would be like, tens of millions of years in the future. But she thought that they wouldn't be happy, to learn they'd left no trace at all.
"I want to talk to you," she said to the Doctor. "Without the lizard people."
"We'll follow you down to the caves!" said the Doctor. "We need to talk about, you know. Mammal things."
"No we don't," said Chris.
The three Earthlings stared awkwardly at them for a while.
"Right!" said Bol, too enthusiastically, "that oil won't survey itself. See you down there, uh—"
"I'm the Doctor; she's Chris."
"They do have strange names, don't they?" said Kala.
"Ha!" said the Doctor. "That's true! We're pretty strange, we are! Ha! Ha ha!"
She laughed for an awfully long time.
"Have they gone yet?" she said eventually.
"A while ago," said Chris.
"Oh, thank God," said the Doctor, whose cheeks were sore from the laughing. "It's awkward, isn't it? Meeting people, and not talking about the total collapse of their civilisation."
"I don't know. But I don't like it when I have to lie."
"It's worth it, though, isn't it? When the truth is very bad."
"That's not what you said to me. When I first saw you; when you were my psychiatrist. You told me the truth, even though no one else would listen."
The Doctor sighed. "But that's not quite the same. You'll've worked it out, of course. Their story has to end so that yours can happen at all. Where there's life, there's hope, but when other lives depend on an ending?" She shook her head. "It's all very different then.
"That's wrong," said Chris. "If you know something that big, even if it's terrible. You should always tell the person that it's about."
"A great many people keeping all sorts from you. That's what being a child is like."
"I know. That's why I think it's a bad thing. And they aren't children, anyway. Everyone's not a child, just because you're really old."
The Doctor looked a bit wounded at that. She glanced down at the Earth, its cities shining like light through an old smashed glass.
"How would you feel," she said, "if someone told you that quite soon all of it would end? That one day the whole world of buses and chairs and houses would just stop, and time would go on like it had never known you were there?"
Chris shrugged. "I wouldn't really care."
The Doctor thought about it. "You wouldn't, no. But lots of people would. And people who grow up to be astronauts and come all the way out here? I think it'll matter a lot to them to believe that their world has a future."
"But that's a lie!"
"It's a truth that they don't know. It's not the same thing."
"I want to go down to the caves now," said Chris, hoping the Doctor noticed how she was too cross to even respond. She was thinking of all the truths the Doctor must know that she would never tell her, when Chris had once thought she was the most honest person in the world. But the worst of it was that the Doctor would still be more honest to her than to most people, that there were lies she'd tell to others without a second thought. She could have been one of those others, if things had been just a bit different. It made it harder to trust the person who was your psychiatrist.
And she came close to having a thought she would need to have very soon: that there was no one the Doctor trusted less than herself. And that meant if a truth was too dreadful to even consider, the Doctor might make sure that she'd never even notice it was there.