We followed him down the steps to that platform. The London Tube had such a reassuring, almost clinical appearance— white-tiled walls with black-tiled edges, neat and distinctive signage, the cheerfully colored map . . . signs showing the

WAY OUT and barriers to keep people moving in the right directions . . . staff in purple-blue suits and computer screens showing the status of trains . . . big ad posters and electronic ad boards that flashed mini-commercials. It didn’t look like something dug out of an old plague pit. It looked like a system that had been here for all of time, pumping people through the heart of the city.

A train had just come in, and the platform emptied out except for us and the handful of people who were too slow. Then I noticed the dark arches at each end of the platform, the openings for the trains leading to the tunnels—the wind that blew in with each train came from there. And when the train left, I noticed one woman in particular down at the far end of the platform. The toes of her shoes were just over the edge. She wore a black sweater with a thick cowl neck, a plain gray skirt, and a pair of gray platform shoes. Her hair was long and curled off her face in large wings. I guess what drew me to her—aside from the fact that she didn’t get on the train and her vaguely retro outfit—was her expression. It was the expression of someone who had given up completely. Her skin wasn’t just pale, it was faint and grayish. She was the kind of person you didn’t see, alive or dead.

“That’s her,” I said.

“That’s her,” Callum confirmed. “She looks like a jumper to me. Jumpers do that a lot, stand on the edge and stare out. Never kill yourself in a Tube station. Tip number one. You might end up down here forever, staring at the wall.”

Stephen coughed a little.

“Just giving advice,” Callum said.

“Go talk to her,” Boo said.

“About what?”

“Anything.”

“You want me to walk up to her and say, ‘Are you a ghost?’”

“I do that,” she replied.

“I love it when you get it wrong,” Callum said.

“Once. It happened once.”

“It happened twice,” Stephen said, looking over.

Boo shook her head and waved me down to the end. I hesitated a moment, then followed a few steps behind until we were next to the woman.

“Hello?” Boo said.

The woman turned, ever so slowly, her eyes wide and sad. She was young, maybe in her twenties. Now I could see her frosted, silvery hair and a heavy silver pendant around her neck. It seemed to weigh her head down.

“We aren’t going to hurt you,” Boo assured her. “I’m Boo. This is Rory. I’m a police officer. I’m here to help people like you. Did you die here?”

“I . . .”