I knew the incident had to be close, though, because I could smell it. It wasn’t truly a smell: it was a painful sharpness in the nose from the plaster dust and smoke and whatever explosive the Germans put in their bombs. It always made Vi sneeze.

I tried to make out landmarks, but all I could see was the slightly darker outline of a hill on my left. I thought blankly, We must be lost. There aren’t any hills in Chelsea, and then realized it must be the incident.

“The first thing we do is find the incident officer,” I told Jack. I looked round for the officer’s blue light, but I couldn’t see it. It must be behind the hill.

I scrabbled up it with Jack behind me, trying not to slip on the uncertain slope. The light was on the far side of another, lower hill, a ghostly bluish blur off to the left. “It’s over there,” I said. “We must report in. Nelson’s likely to be the incident officer, and he’s a stickler for procedure.”

I started down, skidding on the broken bricks and plaster. “Be careful,” I called back to Jack. “There are all sorts of jagged pieces of wood and glass.”

“Jack,” he said.

I turned around. He had stopped halfway down the hill and was looking up, as if he had heard something. I glanced up, afraid the bombers were coming back, but couldn’t hear anything over the anti-aircraft guns. Jack stood motionless, his head down now, looking at the rubble.

“What is it?” I said.

He didn’t answer. He snatched his torch out of his pocket and swung it wildly round.

“You can’t do that!” I shouted. “There’s a blackout on!”

He snapped it off. “Go and find something to dig with,” he said and dropped to his knees. “There’s someone alive under here.”