‘That’s the skipper, Bert Trent, and his first mate, Sid Oliver. They both have top-level security clearance but obviously don’t know what you’ll be up to in Denmark; they only know you as “Tom”. It goes without saying that you don’t breathe a word about your mission while on board. In a moment I’ll give Bert the coordinates for the rendezvous point with the Danish trawler: that’s as much as he needs to know. But he’s absolutely reliable and this isn’t the first time he’s undertaken something like this for us. Here they are.’

The two men who entered the office were both quite short and built like boxers, their weather-beaten faces making it impossible to pinpoint their ages. They moved in the somewhat deliberate way sailors do on land, each smoking a pipe and looking at Prince with a mixture of suspicion and curiosity, studying him without saying a word. Shaw did the introductions and both men crossed the room to shake hands in a rather formal manner. Then he passed Trent an envelope. The skipper put his pipe down while he opened it, read its contents carefully, then handed it to his first mate.

Shaw indicated that they should both join him at a table covered in charts. For a while Trent didn’t say a word as he held a large ruler over the charts and made calculations with a pencil. Then he muttered something to Sid Oliver, who shook his head and pointed to another part of the chart. Trent looked up.

‘It’s very close to Denmark, Jack, very close. They realise that, I presume?’

‘That’s the coordinates we’ve been given, Bert; we can’t change them now. I think it must be because they don’t want to risk the other ship having to come out too far.’

‘I don’t imagine they do. Very well then. The rendezvous point is here – only just outside Danish territorial waters, west of the North Frisian Islands.’ His forefinger tapped part of the North Sea on the map. ‘Sid and I will do more detailed calculations before we set sail, but I’d estimate it being some two hundred and fifty nautical miles from Grimsby. We’ll travel at seven knots; we’re capable of more but that could draw attention to us. Best they see us as a harmless old trawler unable to go any faster.’

‘When will we get to the rendezvous point?’