Mags had brought him back to the lighthouse with her. We sat together in the lantern room, and she brought us up a tray of tea and two buttered slices of fruitcake before disappearing back to the kitchen. I was glad she didn’t stay. There were things I wanted to ask the detective that would have upset or embarrassed my sister, and perhaps she felt the same.

Pinstripe told me that he had had suspicions about Mrs Baron and her son for some time – he’d been sure they were linked to the acts of sabotage. It turned out that Mrs Baron’s husband had been a member of the British Union of Fascists. He had even taken his family to one of Hitler’s rallies in Germany. Mrs Baron moved away from London after his death, somehow managing to conceal her own political beliefs from the authorities. For the last year or so, she and Michael had been working to help prepare for the invasion. She had been taking orders from a friend of her husband in Berlin – sending him packages of information and coded messages via a secret collection point – the telephone box on the Dover Road.

‘The piece of paper you left at the police station gave us an important breakthrough,’ Pinstripe said. ‘The one you left with the constable on the night you reported Michael Baron.’ He settled himself into the wicker chair with his cup of tea and smiled at me. ‘An excellent bit of detective work there.’

‘It wasn’t me,’ I said. ‘It was Grandpa Joe.’

‘Ah.’ Pinstripe took the scrap of paper from his pocket. ‘Well, it was vital evidence. We knew when and where the packages were arriving in London, so as soon as we received this list, we knew Mrs Baron had been at the drop-off point on exactly those days.’

I looked at the scrap of paper, amazed that it had turned out to be useful after all. ‘I didn’t think the policeman was going to give it to you,’ I said, remembering the sneer on Oily’s face as he suggested that I was just a spiteful little girl.

‘He didn’t at first,’ Pinstripe admitted. ‘But when I arrived at the police station later that evening, he told me that the scruffy child from the lighthouse had been in with some tall tale about the magistrate’s son, and that she had had the cheek to bother him with this bit of scribbled nonsense.’

I blushed at the bit about being scruffy.