“Humility is overrated.” He smiled. “It’s a big area to cover. There’s a whole world down here. The Tube itself has about two hundred and fifty miles of track, but the majority of what I do concerns the parts that are actually underground, about one hundred and twelve miles of functional track, plus all the unused tunnels and service tunnels.”

The train whizzed along. All I could see out of the windows was dark, and occasionally the suggestion of the brick walls of the tunnel around us.

“This station we’re going to is one I work at a lot. They know me. It was the site of the largest loss of life in any Tube station, anywhere on the network. It was used as an air raid shelter during the war. One night, they were testing antiaircraft weapons near here—a secret test. The people heard what sounded like an air raid and ran like hell for this station. Someone tripped and fell on the stairs, and soon hundreds of people were crushed in the stairwell. A hundred and seventy-three people died, and a lot of them seem to have stuck around.”

With that, the recorded voice announced that we were pulling into Bethnal Green. When we got off, the station was extremely quiet. A man with a large belly and a face full of broken capillaries was waiting on the platform.

“All right, Mitchell,” he said with a nod. “Who’s she?”

“In training. She’ll stay on the platform. What’s the problem?”

“Eastbound track. They get to the train stop. Then they stop moving, no matter how fast they’re going.”

Callum nodded, like he knew exactly what this meant.

“All right. Normal rules apply.”

“Right.”

The man walked off, leaving us.

“What are the normal rules?” I asked.

“He walks away and has a tea break and doesn’t ask any questions.”

Callum set his bag down on the station platform and removed his jacket, then jumped up high, throwing the jacket over the CCTV camera pointed at the end of the track.

“Do the same with your coat to the one down there,” he said, pointing me to a camera toward the middle of the platform.

I took off my coat and got under the camera. It was up pretty high, but I managed to get my coat over it after a few throws. Callum went to the far end of the platform, where there was a safety gate about chest high. It was loaded down with safety signs. Everything about this gate said, “No. Don’t. Go back. Wrong. Death is certain beyond this point.” Callum opened the gate, which gave access to a few steps that led down to the track level.