When Max looked at him blankly, he added, ‘What happens here is business, Max. Profit, loss. We get our prisoners to help out on our production lines: they get to stay alive, for now, and we get the labour for free. It’s a good system, yes?’

‘Yes, Father,’ Max answered without hesitation.

And he wouldn’t have given the men much more thought. He had, after all, seen plenty of men like them at Dachau, and seeing them here barely made him flinch. This was the way it was. The way it should be. He understood that.

But then he spotted someone. He knew that face. Even when the man wasn’t looking directly at Max – hadn’t even seen him. Even on a body now a quarter of the man he had been, even with the bald head, the hollow cheeks, the lifeless expression just like all the others who Max had long ceased to see as fellow human beings. He knew that face.

Mr Grunberg. Leo’s father.

Max felt rage stir inside him. Why was this man in front of him again? First Dachau and now here? Had he been sent to taunt him? This ghost of his childhood, following him around wherever he went? How dare he?

Then Max pushed his rage down, as a good soldier should, and thought again about the man in front of him. He wasn’t a ghost or a joke. No, he was simply a trial. Just like the letters from Leo and that old photograph that his father had made him burn. Max wouldn’t be surprised if his father had brought Mr Grunberg here himself. Whatever the reason, Max knew what was happening. He was being tested to make sure that he was fully deserving of his place in the regime.

Well, he wasn’t going to fail a test like that.

So, before the man caught his eye and forced him to acknowledge any glimmer of recognition, Max turned away and hurried to keep up with his father.

They walked back up the platform again and his father pointed at the wooden carriages trundling towards them. ‘New arrivals,’ he said. ‘It’s going to get busy here soon. Let’s get back to my office and have some lunch.’

Max marched beside his father without another word, other than to shout out his ‘Heil Hitler!’ salute to each soldier they passed.

And if a tiny voice in his head questioned whether he should have acknowledged Mr Grunberg in some way, even just with a tiny nod of greeting, a much bigger voice replied: it was safer this way. Just as it had been safer to leave Vienna and start again in Munich, all those years ago. Just as it had been safer to burn the photograph and the letters from Leo.