The sound in Macke’s earphone started up as they drove cautiously along a street of five-storey tenements. The area was taking a terrific pounding and several buildings were newly demolished. Werner said shakily: ‘We’re in the middle of the target area, for Christ’s sake.’

Macke did not care: tonight was already life or death to him. ‘All the better,’ he said. ‘The pianist will imagine he doesn’t need to worry about the Gestapo, in the middle of an air raid.’

Wagner stopped the car next to a burning church and pointed along a side street. ‘Down there,’ he said.

Macke and Werner jumped out.

Macke walked quickly along the street with Werner beside him and Wagner behind. Werner said: ‘Are you sure it’s a spy? Could it be anything else?’

‘Broadcasting a radio signal?’ Macke said. ‘What else could it be?’

Macke could still hear his earphone, but only just, for the air raid was cacophonous: the planes, the bombs, the anti-aircraft guns, the crash of falling buildings and the roar of huge fires.

They passed a stable where horses were neighing in terror, the signal growing ever stronger. Werner was glancing from side to side anxiously. If he was a spy, he would now be afraid that one of his colleagues was about to be arrested by the Gestapo – and wondering what the hell he could do about it. Would he repeat the trick he used last time, or think of some new way of giving a warning? If he was not a spy this whole farce was a waste of time.

Macke took out the earpiece and handed it to Werner. ‘Listen,’ he said, continuing to walk.

Werner nodded. ‘Getting stronger,’ he said. The look in his eyes was almost frantic. He handed the earpiece back.

I believe I’ve got you, Macke thought triumphantly.

There was a thunderous crash as a bomb landed in a building they had just passed. They turned to see flames already licking up beyond the smashed windows of a bakery. Wagner said: ‘Christ, that was close.’

They came to a school, a low brick building in an asphalt yard. ‘In there, I think,’ said Macke.

The three men walked up a short flight of stone steps to the entrance. The door was not locked. They went in.

They were at one end of a broad corridor. At its far end was a large door that probably led to the school hall. ‘Straight ahead,’ said Macke.

He drew his gun, a 9mm Luger pistol.

Werner was not armed.

There was a crash, a thud, and the roar of an explosion, all terrifyingly close. All the windows in the corridor smashed, and shards of glass rained on the tiled floor. A bomb must have landed in the playground.

Werner shouted: ‘Clear out, everyone! The building is about to collapse.’

There was no danger of the building collapsing, Macke could see. This was Werner’s ruse for giving the alarm to the pianist.

Werner broke into a run, but instead of heading back the way they had come he went on down the corridor towards the hall.