Ugly though it was, Berliners loved it. When the bombs were falling, its thunder reassured them that someone was shooting back.

Still in a state of high tension, Carla walked from the station to Frieda’s house. It was mid-afternoon, so the Franck parents would probably be out, Ludi at his factory and Monika seeing a friend, possibly Carla’s mother. Werner’s motorcycle was parked on the drive.

The manservant opened the door. ‘Miss Frieda is out, but she won’t be long,’ he said. ‘She went to KaDeWe to buy gloves. Mr Werner is in bed with a heavy cold.’

‘I’ll wait for Frieda in her room, as usual.’

Carla took off her coat and went upstairs, still carrying her bag. In Frieda’s room she kicked off her shoes and lay on the bed to read the battle plan for Operation Zitadelle. She was as stressed as an overwound clock, but she would feel better when she had given the purloined document to someone else.

From the next room she heard the sound of sobbing.

She was surprised. That was Werner’s room. Carla found it hard to imagine the suave playboy in tears.

But the sound definitely came from a man, and he seemed to be trying and failing to suppress his grief.

Against her will, Carla felt pity. She told herself that some feisty woman had thrown Werner over, probably for very good reasons. But she could not help responding to the real distress she was hearing.

She got off the bed, put the battle plan back in her bag, and stepped outside.

She listened at Werner’s door. She could hear it even more clearly. She was too soft-hearted to ignore it. She opened the door and went in.

Werner was sitting on the edge of the bed, head in hands. When he heard the door he looked up, startled. His face was red with emotion and wet with tears. His tie was pulled down and his collar undone. He looked at Carla with misery in his eyes. He was bowled over, devastated, and too wretched to care who knew it.

Carla could not pretend to be heartless. ‘What is it?’ she said.

‘I can’t do this any more,’ he said.

She closed the door behind her. ‘What happened?’

‘They cut off Lili Markgraf’s head – and I had to watch.’

Carla stared open-mouthed. ‘What on earth are you talking about?’

‘She was twenty-two.’ He took a handkerchief from his pocket and wiped his face. ‘You’re already in danger, but if I tell you this it will be a lot worse.’

Her mind was full of amazing surmises. ‘I think I can guess, but tell me,’ she said.

He nodded. ‘You’ll figure it out soon, anyway. Lili helped Heinrich broadcast to Moscow. It’s much quicker if someone reads you the code groups. And the faster you go, the less likely you are to be caught. But Lili’s cousin stayed at the apartment for a few days and found her code books. Nazi bitch.’