Here's what they never tell you about time: it isn't. Not the way other things are. It's impossible to measure, touch, or observe. It only exists relative to other things. Einstein knew. He said, "An hour on a hot stove is an eternity, while an hour with a pretty girl is a moment." It was one of the first things Rory really got when he started learning about time and space.

Einstein might have added that five minutes hanging over a bottomless pit, clinging to a tiny ledge, unable to see anything at all, might as well be five hundred years. Time got really big when it was all you had. Cold trickled down Rory's spine and bit one of his hands; he'd lost a glove at some point. A faint orange glow seemed to build up at the corners of his eyes, only to be blinked away, a mirage. At his back he could hear a regular squeaking, like a corkscrew inside the ice. It worried him a bit. He'd been traveling enough to have a really thorough idea of what might live under the surface of an alien planet. But since that list currently included one Rory Williams, he was afraid to move. The wall at his back was his only point of reference.

Five minutes.

Amy yelped in surprise.

"What?" Rory's heart, which had already been going at a good clip, may have broken the sound barrier. "Amy!"

"It's all right," she said. "It's one of them. The Fa'dkin."

Time started again. "Oh thank God. Tell it we need a torch. And some rope. And a bit of..."

"Babe, I can't tell it anything. It doesn't talk."

"Yeah, but it is intelligent, isn't it?"

"Don't be cross with me, it can hardly... hold on." Snow crunched under Amy's feet, and bits of it fell on Rory's head. "I think that's the Doctor."

"Brilliant," Rory said. Moments later, the chasm was filled with the faintest pastel light. For the first time Rory got something of a look at his position. He regretted it immediately.

The ice shelf hung on the wall of a great deep hole. The pit was perfectly square, and the bottom was lost in shadow. The other three walls were dozens of feet away; you could drop two police boxes down side-by-side and never touch a wall, or even knock Rory off his perch. Above him was a crust of ice and snow, forming a sort of cap over the hole. The light came from the narrow gap through which Rory had fallen.

He hadn't gone down very far at all. He if he dared to stand, could almost reach up and touch the crack. Over time some meltwater and snow had dripped through, forming a horizontal wedge: Rory's fragile shelter.

The wedge settled.

Rory pushed himself away, nearly falling off the opposite side.

"Rory?" It was the Doctor. The shelf settled again. Part of it crumbled and dropped into the hole.

"Stop it!" Rory yelled. The soft whistle from the sonic screwdriver vibrated the ground underneath him. He had to stand to keep from falling off. "Doctor!"

"What's that, Rory?"

"Oy! Stop! Sonic-ing!"

"Right? Right. Of course. Sonic screwdriver—bit of snow—before you know it you've got an avalanche on your hands. Sorry Rory." The light went out. Seconds later, another, light came on. It was orange and flickering. A flame.

"Matches," the Doctor said. "Always carry a box of matches. You never know when you might need a proper fire. Here, you can have this one, Amy. I've got another. Are you all right? Of course you are." Hiss. Splutter. The orange light got brighter, and Rory felt even colder. There was something dreadfully lonely about seeing a distant flame. A single candle can stave off hypothermia. That was another thing Rory had learned in what he considered his post-graduate space survival course.

"Now. Rory. Is there any place down there to land the TARDIS?"

Rory was now standing on half a shelf, facing the wall. What was left of it had gentle slope, and he had to keep pushing with his weak ankle to keep himself upright. He looked carefully over his shoulder. "I don't see anything."

"Great," said the Doctor. "Wonderful. I do love a puzzle."

"Can't you just put it on the path and drop a rope down?" Rory suggested.

"Could do," said the Doctor.

"Then do it." Rory could hear Amy pacing up above. "Let's just go and get him."

"Could do," the Doctor repeated. "But it's a question of physics, isn't it, Rory? A tiny screwdriver rogered your footing. How would you feel about me parking the TARDIS up here?"

The Doctor tapped the path with his foot, and more snow fell on Rory's head. Rory started to say something, but the Doctor interrupted. "I agree. Absolutely not. But—of course! Stupid me. Have you got your key?"

Hope leaped through Rory's heart. He patted his shirt and found his TARDIS key on a lanyard round his neck. He squeezed it with his bare hand. "What?" said Rory. "Are you going to use it beam me up or something?"

It was like Rory had just suggested they put paper bags over their heads. "Are you mentally ill? Did you spend your entire honeymoon watching television? No; I just wanted to say: take care not to lose it. I don't want to spend the rest of the year digging it up."

Rory pressed his head against the wall. He didn't know much about Time Lord history—the Doctor was famously closed-lipped about it—but sometimes he suspected that they'd been irritated to death. He told himself to be patient. When the Doctor was talking, he was thinking, and thinking was good. Probably.

"Let's see: Chvet, south pole, ice caverns, circa fiftieth century with previous human habitation c. forty-eighth..." The Doctor snapped his fingers. "Light! You need more light. A moment. Amy, hold this."

"A jar?" said Amy. There was a clatter from above.

"Matches. And, yes, a jar. Astutely observed. Rory, can you still hear me?" The Doctor's voice was more distant.

"A bit." This sounded promising.

"Get as close to the wall as you can."

Rory already was as close to the wall as he could be, but he made a show of hugging it.

"Amy," said the Doctor, "tell me you used the oil lamps from the attic."

"Um. Yes?"

"Bless your romantic hearts. Heads up, Rory." Something hit the snow and rolled down the slope. It clattered through the hole, barely missed Rory's head, and plunged into the pit. It looked like a shooting star, but Rory realized it was a bundle of lit matches in a glass jar. It was like a little tiny firebomb. After what seemed like half an age, the fire jar struck the floor. Somewhere down there, Rory's lamp had fallen, spreading oil all over. There was a whuff, and a large fire kindled at the bottom of the hole. The light filtered up to the top, along with the barest breath of heat.

"Ha!" said the Doctor.

Yes, Rory thought, because what this situation really needed was a lake of fire.

"Tell me what you see." The Doctor's voice was intent.

Rory had another look around. The light was brighter and steadier. It flickered off dark wood and bright metal. There was some kind of scaffolding, all around the hole. Most of it was encased in ice, and some of it was rusted or rotting, but Rory knew what it was. "It's a mine shaft."

"A mine shaft!" The Doctor echoed. "A mine shaft."

"Um," said Rory.

"Okay," said the Doctor. "Look around you. Most of the scaffolding is structural, eh? Actually, all of it is. But there's bracing at the corners. Ceramic and, hmm, synthwood. Do you see it?"

Rory didn't see any "synthwood," but there was bracing. Thick wooden beams, gripped at either end by heavy iron clips, formed small triangles against the corners. There was about ten feet between each one.

"Now, all you need to do is use those. Hop down to the bottom; we'll meet you there with the TARDIS, and be off this planet and not a moment too soon. God, I'm good. We're good."

"I'm supposed to hop, am I?" Rory muttered. "Just jump down a mine shaft twenty stories high."

"It's easy if you don't think about it."

Rory was having a lot trouble thinking about anything else. Amy loudly protested, and the Doctor shushed her.

"And look lively," said the Doctor. "That fire will be out in about three minutes. See you in a tick."