‘He could be executed for that,’ Frieda said.

‘If we knew someone who could get in touch with Moscow, we might turn the course of the war,’ Carla went on, as if still talking about the gravity of Joachim’s crime.

‘Perhaps,’ said Frieda.

That proved it. Frieda’s normal reaction to such a story would include expressions of surprise, lively interest, and further questions. Today she offered nothing but neutral phrases and noncommittal grunts. Carla went home and told her mother that her intuition had been correct.

Next day at the hospital, Frieda appeared in Carla’s ward looking frantic. ‘I have to talk to you urgently,’ she said.

Carla was changing a dressing for a young woman who had been badly burned in a munitions factory explosion. ‘Go to the cloakroom,’ she said. ‘I’ll be there as soon as I can.’

Five minutes later she found Frieda in the little room, smoking by an open window. ‘What is it?’ she said.

Frieda put out the cigarette. ‘It’s about your Lieutenant Koch.’

‘I thought so.’

‘You have to find out more from him.’

‘I have to? What are you talking about?’

‘He has access to the entire battle plan for Case Blue. We know something about it, but Moscow needs the details.’

Frieda was making a bewildering set of assumptions, but Carla went along with it. ‘I can ask him . . .’

‘No. You have to make him bring you the battle plan.’

‘I’m not sure that’s possible. He’s not completely stupid. Don’t you think—’

Frieda was not even listening. ‘Then you have to photograph it,’ she interrupted. She produced from the pocket of her uniform a stainless-steel box about the size of a pack of cigarettes, but longer and narrower. ‘This is a miniature camera specially designed for photographing documents.’ Carla noticed the name ‘Minox’ on the side. ‘You’ll get eleven pictures on one film. Here are three films.’ She brought out three cassettes, the shape of dumbbells but small enough to fit into the little camera. ‘This is how you load the film.’ Frieda demonstrated. ‘To take a picture, you look through this window. If you’re not sure, read this manual.’

Carla had never known Frieda to be so domineering. ‘I really need to think about this.’

‘There’s no time. This is your raincoat, isn’t it?’

‘Yes, but—’

Frieda stuffed the camera, films and booklet into the pockets of the coat. She seemed relieved they were out of her hands. ‘I’ve got to go.’ She went to the door.

‘But, Frieda!’

At last Frieda stopped and looked directly at Carla. ‘What?’

‘Well . . . you’re not behaving like a friend.’

‘This is more important.’

‘You’ve backed me into a corner.’

‘You created this situation when you told me about Joachim Koch. Don’t pretend you didn’t expect me to do something with the information.’

It was true. Carla had triggered this emergency herself. But she had not envisaged things turning out this way. ‘What if he says no?’

‘Then you’ll probably be living under the Nazis for the rest of your life.’ Frieda went out.