“So that explains why her TARDIS looked like a police box,” the Doctor said to Yaz, later that day when they’d both returned to their flat. “For the same reason mine did, way back when. She was just hiding out in London in the sixties. A place where it would actually be a disguise.”
“Same reason as the COPS, too, come to think of it,” she said. “Isn’t life funny, Yaz? Full of coincidences.”
Yaz fidgeted awkwardly.
“Yeah,” she said. “Coincidences.”
She took a deep breath.
“Although you have to be sure a coincidence is all it is,” she said. “When you’re a police officer.”
“Then it’s a good job that both of us are sure,” said the Doctor, just a note too sharply.
“That you both just came to the same city at the same time,” said Yaz. “To the same planet. When something massive in history was going on.”
“I came here a year later,” said the Doctor. “It doesn’t fit. Coincidences do happen, Yaz. It’s easy to make too much of them.”
“Doctor,” said Yaz firmly. “Imagine you’re wrong about what happened here. And I’m not saying you are, but if you were— what does it look like?
If the end of the world… if it was supposed to have happened?”
The Doctor furrowed her brow.
“Then it’d have found a way to happen anyway,” she said. “The universe has a way of putting things straight. Making sure things happen the way they’re supposed to, more or less.”
“A nuclear war?”
The Doctor shook her head.
“Doesn’t have to be exact,” she said. “Just something that wipes you out. Like a virus, or climate change, or”—
“Aliens?” said Yaz, very quietly.
The Doctor stopped talking abruptly. She stared back at Yaz, horror in her eyes.
“Not that!” she said. “This has nothing to do with”—
“What if it does?” said Yaz, firmly.
“Then history would make it so that”—
The Doctor stopped talking again as the colour drained from her face.
—“so that aliens attacked the planet and made it die. But if they didn’t succeed; if somebody stopped them? More aliens would attack, again and again. They wouldn’t stop coming ‘till the day that they finally won. But that’d be because of… it’d all come back to here. And if the thing that stopped the aliens was the same thing that stopped this crisis… she might not even notice that anything had gone wrong…”
Hands shaking, she drew the long, thin Geiger counter from her pocket.
“Let’s turn this on,” she muttered softly. “There’s somewhere that I haven’t checked.”
“Give it to me,” Yaz said, gently. “You don’t have to face stuff alone.”
The Doctor shook her head, though only slightly.
“I can do this,” she said. “Really. I can.”
She held the Geiger counter out in her hand, so it was facing the world outside— then slowly turned it around, so the bulb was held up to her chest.
She swallowed, and turned the counter on. And at first there was nothing, just the breathing of them both. But as they waited a slow beep started to come from the device, growing more rapid and then more furious, until it was a low and dreadful drone like the scream of a dying star—
The Doctor looked back up at Yaz, her expression one Yaz knew too well. The same as a parent’s, just after you’d told them. The face they made when they knew that their child would never come back.
“Yaz,” she said.
Yaz knew what she was going to say, of course. But that was another thing you had to know when you were a police officer. Sometimes you had to say things to someone, even though you both knew them already.
“I was wrong,” she said. “It was never supposed to blow over, not really. The Cold War should never’ve stayed so cool. October 1962, before the month is out. London burns; your species dies. Except it doesn’t, because somebody stopped it.”
She looked Yaz hard in the face.
“And it was me.”