‘We were beginning to think that maybe he’d pulled a fast one on us – by which I mean that despite our best endeavours he’d somehow managed to slip a warning signal in one of his messages to the Germans. In fact, we were considering giving up on him and handing him over for trial. Then one week ago, he was contacted by Berlin. An agent called Poacher would be arriving in England in the next few days. A U-boat would drop him off the Lincolnshire coast, and once safely ashore, Laurens would receive a telephone call with an agreed code word. He was then to let Berlin know Poacher had landed safely and wait for him to arrive in London.

‘Laurens was told Poacher would reach London within forty-eight hours of his initial telephone call, at which point he’d contact him and they’d meet at a pub called the Thornhill Arms. It’s on the Caledonian Road, only a few minutes’ walk from King’s Cross, which is the mainline station you’d arrive at from Lincolnshire, so that all fits. Laurens was then to bring Poacher back to his house in Clapham, keep him there for a few days, make sure he had enough money and the right documentation – ration cards and the like – and drive him down to Portsmouth. We think he may have a contact there, so it was essential for us to let him get there. If there is indeed a Nazi cell operating in our largest naval port, we’d rather like Poacher to introduce us to it.’

The man with the Scottish accent paused and looked at Prince, who’d clearly absorbed the information in a way the Chief Constable hadn’t. He smiled, indicating he was finding the story interesting rather than one he felt he had to pick holes in.

‘And Poacher has disappeared?’ He was well-spoken, his voice strong.

‘Why that presumption, Prince?’

‘Otherwise you wouldn’t be visiting us, would you?’

‘We know Poacher must have arrived in the early hours of Monday morning because Laurens received a telephone call that lunchtime with the correct code word to indicate his safe arrival. And at low tide that evening the shore patrol spotted a section of barbed wire that had been cut on the beach just north of Mablethorpe. Do you know the place?’

‘I do, actually.’

‘The actual point was at the northern end of what I understand is called the Town Beach. On the other side of the beach are sand hills and then open fields. The assumption has to be that Poacher landed on the early-morning low tide; the subsequent high tide then washed away his footprints and whatever he landed in. Since then – nothing. Not a whisper.’

‘He’s probably miles away by now. I told our—’