The French group was regarded as one of the most useful as far as the Germans were concerned. Most of them were mechanics or electricians, and they knew how to play the system. They cooperated with the Germans just enough to ensure their work was usually less physically onerous than that of other slave labourers. That wasn’t to say the Germans trusted them. They had an inherent dislike for the French, but they also regarded them as being intellectually smarter than the Russians and the Ukrainians and more able than the Poles.

It was rare for a group to work in the same area for more than a day at a time. ‘Don’t ask me why,’ said Émile. ‘Maybe it’s something to do with minimising the chances of sabotage, or it could be because they don’t want people to gather too much detailed information about what’s going on here.’

It was common knowledge in the camp that this was where the V-1 and V-2 rockets were being developed and manufactured. The slave labourers talked about them openly.

‘The Germans know there’s only one way we’ll leave this camp alive.’

‘What’s that, Émile?’ They were in their hut after what passed as the evening meal and the final roll call. It was bitterly cold, the wind whistling through gaps in the wood, a single layer of which was all that stood between them and the Baltic.

‘If they win the war – which they think they will do with these rockets. If they don’t win, they’ll kill us.’ The other men nodded in a matter-of-fact manner.

‘Even if they do win the war,’ said Alain, ‘we’ll be dead by then. How much longer do you think we can survive in these conditions?’

Prince asked a few more questions while they were gathered together: he needed to get on with his map of the camp. Where did they think the power station was and the main rocket test fire area?

They all joined in with their advice. He was now building up a good picture of the layout.

‘We’re helping to sign our own death warrant.’ It was Alain again, one of the few men not from Tours.

‘In what way?’

‘What do you think they’re going to use your map for, Mister Churchill? To put on Christmas cards? No, they’ll use it to bomb this place.’

‘Good,’ said Émile. ‘Just make sure you clearly mark where we are – and maybe ask them not to bomb that part!’

By 24 January, Prince believed he had as much information about the camp as he was going to get. He took out a sheet of paper he’d been hiding under his straw mattress and managed to sharpen his pencil using a stone. He’d been drawing for ten minutes when Alain came over.

‘That’s shit. You can’t draw. Give it to me, I’ll do it.’