After that intitial meeting, the families took all their meals together and walked the mountains together. Over supper each night their fathers talked about the increasing persecution of Jews in Germany. It was the reason Heck’s father had moved them from Bavaria back to Amsterdam, their home city, a year earlier. Solomon Rabinowitz wouldn’t have it, though. Berlin was his city, he said, and he was damned if some pipsqueak corporal with a loud voice and an ugly moustache was going to make him give up his beloved home and medical practice. ‘They won’t be there forever,’ Rabinowitz said. ‘It’s just a matter of waiting them out. Germany is fundamentally a civilised country. You’ll see.’

‘But you can’t even practise your craft, Solomon,’ Maurice Heck replied.

‘But I can still treat my own people – our people – and they need me, now more than ever.’

Mozes and Miriam heard these dark conversations, and they were old enough to understand. They had felt the coming darkness themselves. It seemed to them that Jews were being punished for some unspecified crime. Certainly, their lives had already changed. Miriam had been removed from her school and was being educated at home. More than that, they understood that the situation was dangerous.

But none of it really mattered to Mozes Heck and Miriam Rabinowitz. All they cared about was each other. At the end of the two weeks, they kissed. It was a new and thrilling experience for both of them. They took their addresses and wrote to each other at least once a week until May 1940.

After that, Heck escaped to England and heard no more, either from his own family or the Rabinowitzes. Often he wished that both sets of parents had had the sense back in 1937 to stay in Switzerland and seek asylum, or perhaps take a direct flight to London.

If only.

He raised his hand to knock at the door. He was aware of the ‘U-boats’, the Jews who had stayed in Berlin and other parts of Germany, avoiding deportation to the death camps by surviving beneath the surface. He was aware, too, that precious few of them had made it to the end of the war; too many Germans were prepared to denounce their neighbours.

And if by a miracle they had survived, where would they be now? Perhaps they had come home? Perhaps they had somehow managed to stay here all along. This tenement block, this apartment was the only lead he had.

He knocked, and heard scuttling inside, like rodents scurrying to their holes. He knocked again. This time he heard a voice from the other side of the door.

‘Who is it?’ A woman’s voice.

‘Heck. Mozes Heck, from the holiday in Switzerland.’

‘Who?’

‘Can you open the door, please?’

‘Go away.’