Lunch was strained. Carla and Maud ate a thin soup made with a ham bone and dried peas. Carla did not ask what Maud had done, or promised to do, to persuade Koch. Perhaps she had told him he was making marvellous progress on the piano but could not afford to miss a lesson. She might have asked whether he was so junior that he was monitored every minute: such a remark would sting him, for he pretended constantly to be more important than he was, and it might easily provoke him into showing up just to prove her wrong. However, the ploy most likely to have succeeded was the one Carla did not want to think about: sex. Her mother flirted outrageously with Koch, and he responded with slavish devotion. Carla suspected that this was the irresistible temptation that had made Joachim ignore the voice in his head saying: ‘Don’t be so damn stupid.’

Or perhaps not. He might see sense. He could show up this afternoon, not with a carbon copy in his bag, but with a Gestapo squad and a set of handcuffs.

Carla loaded a film cassette into the Minox camera, then put the camera and the two remaining cassettes in the top drawer of a low kitchen cupboard, under some towels. The cupboard stood next to the window, where the light was bright. She would photograph the document on the cupboard top.

She did not know how the exposed film would reach Moscow, but Frieda had assured her it would, and Carla imagined a travelling salesman – in pharmaceuticals, perhaps, or German-language Bibles – who had permission to sell his wares in Switzerland and could discreetly pass the film to someone from the Soviet Embassy in Bern.

The afternoon was long. Maud went to her room to rest. Ada did laundry. Carla sat in the dining room, which they rarely used nowadays, and tried to read, but she could not concentrate. The newspaper was all lies. She needed to cram for her next nursing exam, but the medical terms in her textbook swam before her eyes. She was reading an old copy of All Quiet on the Western Front, a German bestseller about the First World War, now banned because it was too honest about the hardships of soldiers; but she found herself holding the book in her hand and gazing out of the window at the June sunlight beating down on the dusty city.

At last he came. Carla heard a footstep on the path and jumped up to look out. There was no Gestapo squad, just Joachim Koch in his pressed uniform and shiny boots, his movie-star face as full of eager anticipation as that of a child arriving for a birthday party. He had his canvas bag over his shoulder as usual. Had he kept his promise? Did that bag hold a copy of the battle plan for Case Blue?

He rang the bell.

Carla and Maud had premeditated every move from now on. In accordance with their plan, Carla did not answer the door. A few moments later she saw her mother walk across the hall wearing a purple silk dressing gown and high-heeled slippers – almost like a prostitute, Carla thought with shame and embarrassment. She heard the front door open, then close again. From the hall there was a whisper of silk and a murmured endearment that suggested an embrace. Then the purple robe and the field-grey uniform passed the dining-room door and disappeared upstairs.