The door opened and a man hurried into the room, muttering what could possibly have been an apology had it been at all clear before taking a seat alongside the Chief Constable, opposite the Scotsman.

‘Ah… at last. This is Detective Superintendent Prince. Richard Prince. I was telling you about him. Perhaps, for his benefit, you could tell us again about the purpose of your visit?’

The man caught the gaze of Detective Superintendent Prince. He was notably younger than he’d expected, probably no more than his mid-thirties, and with what his wife would insist on describing as matinee idol looks. He certainly had a presence about him, and a purposeful stare. He sat quite still, with a very slight air of superiority about him. The Chief Constable had already told him Richard Prince was the best detective on his force – indeed, by far the best one he had ever worked with.

‘Very well then, Prince: you will of course respect the very confidential nature of what I am about to say.’

The Scotsman leaned forward in his chair, and as he did so, his face caught the light above him, showing the ruddy, lined appearance of someone who’d spent a considerable time out of doors.

‘Some eight months ago, we arrested a Dutch national in south London. Let’s call him Laurens. We’d been on his track and knew he’d been sent over as a Nazi spy, specifically to be a point of contact between other Nazi agents in this country and their controllers back in Germany: a radioman. It has been our policy – where appropriate – to turn such spies to our advantage. Where we think it is feasible, we offer them a choice: they can stand trial for espionage and if found guilty expect the inevitable death sentence. Or they can allow themselves to become double agents, to work for us. We don’t offer this to every Nazi spy, and it’s not without its risks. But in the case of Laurens, it made sense.

‘In the early part of the war, the Germans did send over quite a number of agents, but they were a pretty second-rate bunch and we’re confident we captured all of them. Since late 1940, early 1941, the number being sent over has dropped off noticeably, and in the eight months that Laurens has been with us, no agents have been in contact with him.