I thought back to Mutti’s letter – Remember that I have told the policeman everything he needs to know. I am ready now to tell them that it was me, to write it down and sign it. I’m so sorry, my darlings. This is the best way. I love you all so much. This had been her coded message to Mags. Her way of telling her daughter that she was taking the blame, and warning her to keep quiet.

‘Mutti was right in a way, though, wasn’t she?’ I said. ‘Mags was helping the Barons to prepare for the enemy landing – although she didn’t really know it.’

‘It’s her naivety that has saved your sister from prosecution,’ he said. ‘Sadly, your father made a conscious decision – he gave in to Mrs Baron’s blackmail in an attempt to protect your mother.’

‘I haven’t told the others,’ I said then. ‘I haven’t told anyone what Pa did.’

Pinstripe looked at me strangely. ‘How did you know about it, Petra? How did you know that he was responsible for sending the documents?’

I nodded towards the speaking tube. ‘I found out about Pa in the same way that you heard Mrs Baron’s confession – through the speaking tube,’ I said. ‘The day before Dunkirk. I heard Pa tell you the truth.’

Pinstripe smiled a little. ‘Well, there’s no reason for anyone to know now,’ he said slowly. ‘They’ll find out soon enough what Mrs Baron did. They’ll know that your sister was manipulated by Michael Baron, and that your mother is completely innocent. Let them remember your father as the man who saved the lives of many, many people – with his lighthouse and his lifeboat.’ He looked straight at me and crinkled his craggy brow. ‘But that’s a very heavy secret to carry around all by yourself, Petra.’

‘Yes,’ I said. ‘But I’m strong enough to carry it.’

We sat quietly for a while, watching the steady roll of the whale-grey waves. The U-boat had gone, but its cold, threatening presence somehow remained – lurking there in the murky water, just like the Wyrm. But, for now, there will be no more sacrifices, I thought. For now, those monstrous, writhing shadows will have to stay hungry.

I often think about the song I sang when I was sitting up on the cliffs, waiting for Pa and Mags to return from Dunkirk. In the smoky light of that dawn, a spell was woven that would bind me to the magic of the clifftops and the stones for ever. The doctor says that the feeling in my legs could come back any day, or it may never come back at all. I try not to think about it. Instead, I think about how proud I am.