Omega was frowning when the two of them came through the TARDIS doors. Somehow he'd managed to make several parts of the console give out biscuits— except for the custard cream dispenser, which was leaking oil.
"Mind it, Omega!" said the Doctor. "This TARDIS isn't yours. You can't go messing with all the buttons and stuff. You'll give the poor thing a headache. And it's the worst kind of headache, probably, when you've not even got yourself a head"—
"You've not said where we were going," she added as she remembered.
"Well, we're not going anywhere at all, if you don't show me round the controls," said Omega. "Most of it's pretty basic, as far as I can see. But tell me. How does this ship go starboard?"
The Doctor frowned.
"Starboard?" she said.
"Waterwise!" cried Omega, as though that explained it. "To the sea beyond the stars. Behind the firmament, or beyond it."
The Doctor made the sort of confused face Yaz was pretty used to doing.
"You mean to say you didn't know?" said Omega. "That no one ever discovered…"
He laughed, shaking his head.
"The Time Lords," he said. "They really weren't anything, without the two of us!"
"Do I have you right?" asked Yaz. "There's an ocean behind space?"
"Well, of course," said Omega. "The darkest deep, where day and night were first divided. The sea where the waters rose from in the floods"—
Yaz's eyes widened.
"Like Noah's Flood?" she said. "The Doctor said that never happened!"
"What happens is only a subset of possibility," Omega said with a twinkle in his eye. "Once you can travel through all of time and space, it doesn't take much to enter something more. Even if this TARDIS was built by people who didn't know that"—
He trailed off, frowning. He was pressing console buttons with one hand while poking a biscuit with the other.
"But it isn't working," he said. "I don't know why."
The Doctor was quiet, almost apologetic.
"I think I do," she said.
She was looking up at the enormous crystal in the console, pulsing orange and dull. Her TARDIS was tiny and blue, unimposing. You'd have no idea what really lurked inside. How gloomy it really was. How offputting. Yaz had figured out what that was about, a very long time ago now.
"I was thinking about what you said, about the void," the Doctor said to Omega. "And you're right. There's so much darkness out there. More than a human mind could ever see. So much of it that if you stopped being careful—
She smiled, and pressed her hand against the console.
—"you might forget that you can see the sky," she said.
The orange light was already brightening as she closed her eyes. Like a dawn was breaking, like a sunrise. By the time the Doctor had opened them again, the console's crystal was as pale and as blue as her coat.
"Now we can go," she said.
Omega flipped a switch and the TARDIS wheezed and moaned—
—and slowly the wheezing turned into a different noise. A long, low bass, inhaling and exhaling. The sound of a giant slowly beginning to breathe. It made the floor vibrate along with their bones. The ship was humming, and it felt like the world was as well.
"You know something," said Omega under the sound. "I think I'm happy. I'm actually happy! I've no idea how long it's been."
"Well, you're a free man now," laughed the Doctor. "Omega Free! Like the fatty acid. And also good for you"—
"You don't have to explain your jokes all the time," said Omega." I am a genius, in case you've already forgotten."
Doctor looks at him, mock affronted.
"Cheeky," she said. "Y'know, I think I might've preferred you when you were evil."
This was how it was going to be with the pair of them, Yaz realised. Bickering like old ladies on the bus. It'd drive her mad, and she wouldn't trade it for anything else in the world.
She smiled, and decided not to say anything. But now, she knew she really was making a choice.
The sound of crashing waves echoed around them. They were at the threshold of the sea beyond all things.
"It's time," said the Doctor. "The three of us; we've been cooped up in our universes for far too long. Today is the day that isolation ends. And we're going—
—the breath of the TARDIS roared—
—"where we've always wanted to go"—
—the sound of the waves broke and boomed—
—"outside," she said.
Then something impossible happened, and they were gone.