‘Perhaps it fell out,’ I said, aware that my voice sounded stone-cold, and I didn’t know if it was because I was so angry with her, or if it was because I was lying. ‘It probably fell out as we were going down the tunnel.’ And you didn’t notice, I wanted to add, because you were so bewitched by Michael blooming Baron. My hand closed guiltily around the paper in my pocket, crushing it into a ball.

It was a strange, silent walk back up to the Castle. I couldn’t bring myself to say anything to Mags at all, and, for the rest of the day, I could barely even look her in the face. Anger, doubt and suspicion were billowing in my mind like storm clouds.

When I came down to breakfast the next morning, there was a letter from Mutti waiting on the kitchen table. Pa must have just opened it, and was staring at it as if it had bitten him.

‘Can I read it?’ I asked.

Pa took a breath, and then nodded. ‘Of course, Pet – it’s to all of us.’

‘I’ll read it out loud,’ Mags said, appearing from behind me and snatching it out of my hand. I hated it when she did her Big Sister act. On top of everything else that had happened recently, it made me feel like giving her an almighty shove, but Pa looked upset enough already, so I just shot her one of my foulest looks and went to sit at the other end of the table.

I tried to push all the terrible thoughts to one side and listened.

‘Dearest Fred, Mags and Pet,

‘My darlings, I have been told that once a week I may write to you. I have been given this paper and told that I might write, but I am not allowed to write very much, so I shall (from now) try not to waste any words! I am well. It is quite comfortable here and clean enough, and the food is not too bad, but I am missing eating our home-grown vegetables. There are lots of people here who are kind and someone even shared a piece of chocolate with me yesterday. I have met a lady who is from Munich, near where I grew up. It has been very pleasant to speak in German for the first time in so long.

‘There is a police inspector investigating the diagrams they showed me in court. He has been here to see me. He is a very nice man, and also clever. He may come to see you all at the Castle, so please do be helpful, but remember that I have told him everything he needs to know.’

At this point, Mags’s brow furrowed. ‘What does that mean?’

She looked down again and read on.