Macke shrugged. ‘Tradition.’

A black curtain divided the room in two. Macke drew it back to show eight hooks attached to an iron girder that ran across the ceiling.

Werner said: ‘For hanging?’

Macke nodded.

There was also a wooden table with straps for holding someone down. At one end of the table was a high device of distinctive shape. On the floor was a heavy basket.

The young lieutenant was pale. ‘A guillotine,’ he said.

‘Exactly,’ said Macke. He looked at his watch. ‘We shan’t be kept waiting long.’

More men filed into the room. Several nodded in a familiar way to Macke. Speaking quietly into Werner’s ear, Macke said: ‘Regulations demand that the judges, the court officers, the prison governor and the chaplain all attend.’

Werner swallowed. He was not liking this, Macke could see.

He was not meant to. Macke’s motive in bringing him here had nothing to do with impressing General Dorn. Macke was worried about Werner. There was something about him that did not ring true.

Werner worked for Dorn; that was not in question. He had accompanied Dorn on a visit to Gestapo headquarters, and subsequently Dorn had written a note saying that the Berlin counter-espionage effort was most impressive, and mentioning Macke by name. For weeks afterwards Macke had walked around in a miasma of warm pride.

But Macke could not forget Werner’s behaviour on that evening, nearly a year ago now, when they had almost caught a spy in a disused fur coat factory near the East Station. Werner had panicked – or had he? Accidentally or otherwise, he had given the pianist enough warning to get away. Macke could not shake the suspicion that the panic had been an act, and Werner had, in fact, been coolly and deliberately sounding the alarm.

Macke did not quite have the nerve to arrest and torture Werner. It could be done, of course, but Dorn might well kick up a fuss, and then Macke would be questioned. His boss, Superintendent Kringelein, who did not much like him, would ask what hard evidence he had against Werner – and he had none.

But this ought to reveal the truth.

The door opened again, and two prison guards entered on either side of a young woman called Lili Markgraf.

He heard Werner gasp. ‘What’s the matter?’ Macke asked.

Werner said: ‘You didn’t tell me it was going to be a girl.’

‘Do you know her?’

‘No.’

Lili was twenty-two, Macke knew, though she looked younger. Her fair hair had been cut this morning, and it was now as short as a man’s. She was limping, and walked bent over as if she had an abdominal injury. She wore a plain blue dress of heavy cotton with no collar, just a round neckline. Her eyes were red with crying. The guards held her arms firmly, not taking any chances.

‘This woman was denounced by a relative who found a code book hidden in her room,’ Macke said. ‘The five-digit Russian code.’