Cristina came down the steps and shut the iron trapdoor behind her with a clang. “How did the police get onto us?” she said.

“The Stasi were following my girlfriend.”

“You stupid fool, you’ve betrayed us all.”

“Then I’ll go last,” Walli said.

The male student went down the shaft, and Cristina made to follow.

“Give me your gun,” Walli said.

She hesitated.

Walli said: “If I’m behind you, you won’t be able to use it.”

She handed it to him.

He took it gingerly. It looked exactly like the pistol his father had pulled from its hiding place in the kitchen, the day Rebecca and Bernd had escaped.

Cristina noticed his unease. “Have you ever fired a gun?” she said.

“Never.”

She took it back from him and moved a lever near the hammer. “Now the safety catch is off,” she said. “All you do is point it and pull the trigger.” She put the safety catch on again and handed the gun back to him. Then she went down the ladder.

Walli could hear shouts and car engines outside. He could not guess what the police were doing, but it was clear he was running out of time.

He saw how things had gone wrong. Hans Hoffmann had had Karolin under surveillance, no doubt hoping that Walli might come back for her. The tail had seen her meet a boy and go off with him. Someone had decided not to arrest them immediately, but to see whether they would lead their watchers to a group of co-conspirators. There had been a slick change of personnel after they got off the bus, and a new follower had taken over, the man in the brown coat. At some point he had realized they were heading for the Wall, and had pressed the panic button.

Now the police and the Stasi were outside, searching the rear of the derelict buildings, trying to figure out where Walli and Karolin had gone. They would find the trapdoor any second now.

With the pistol in his hand Walli went down the shaft, following the others.

As he reached the foot of the ladder he heard the clang of the iron hatch. The police had located the entrance. A moment later there were gruff shouts of surprise and triumph as they saw the hole in the floor.

Walli had to wait a long, agonizing moment at the mouth of the tunnel, until Cristina disappeared inside. He followed her, then stopped. He was slim, and he was just about able to turn in the narrow passage. He peeked out, looking up the shaft, and saw the bulk of a policeman stepping onto the ladder.

This was hopeless. The police were too close. All they had to do was point their guns into the tunnel and fire. Walli himself would be shot, and when he fell the bullets would pass over him and hit the next in line—and so on: the slaughter would be bloody. And he knew they would not hesitate to shoot, for no mercy was shown to escapers, ever. It would be carnage.