Mutti? And that word ‘sacrifice’. For so many years, it had been a word that meant only one thing to me: four girls on a clifftop singing to the sea. Four girls who offered up their lives to save others. In that moment, I was aware of the Daughters of Stone outside on the clifftop, sparkling darkly, calling to me as one of their own – giving me strength. So many lives were at risk now – it wasn’t just Mags and my Pa, as it had been at the dawn of Dunkirk. Now it was the harbour, Dover, the white cliffs; it was every soul who lived along our coast. If the landing was successful, it could be every soul in England.

The song of the stones became almost dizzying, like a fingertip running around the rim of a brandy glass – high, resonant and piercing – a siren. And somewhere below the sound, somewhere far below the lantern room, there was another sound. A murmur of voices, and a little dry sound, rather like the cough of a fox.

It can’t be . . .

Mrs Baron watched the hypnotic beam of light and, while she was facing away from me, I did the only thing that I could do. I hauled myself forward in the chair, stretching out as far as I possibly could, fingers reaching, reaching, until I caught the brass end of the speaking tube with my fingertips and brought it quickly to my mouth. I blew as hard as I could through the tube, praying that the whistle was fitted to the other end. Sure enough, the shrill sound echoed up from the kitchen. Mrs Baron spun around and strode towards me to swat the speaking tube from my hands. It clattered loudly to the floor.

‘What are you doing, you stupid girl? Do you think that will stop me? There is no one at the other end. No one to help you. Your grandfather is in Dover. Your stupid sister is unconscious. Your father is dead. Your mother is locked up, miles and miles away from here.’ Her voice swelled with manic pride. ‘I knew that she was innocent, of course, and I am sorry about what happened. But it was better to have her locked up than to risk losing the real collaborator – the one I needed – the one who was capable of passing on such useful information direct from the Admiralty.’

‘Pa,’ I breathed. ‘You knew Pa was the spy?’

‘Of course I knew it was him. I made him do it.’

What?