The blurb says

GERMANY 1941. It was the most incredible plan. No one gave them the chance. British officers Hugh Hartley and Malcolm Royce achieved what some believed to be impossible and escaped from the infamous Oflag IVc –– Colditz Castle. But as they are about to cross the Swiss border, Royce is shot. He begs Hartley to save himself and, wracked with guilt, Hartley leaves his friend behind.

LONDON 1973. Hartley is a senior MI6 officer and shadowy contact tips him off that Royce could still be alive and being held in Colditz –– now a lunatic asylum. Desperate to know what really happened to his comrade, Hartley sets out an a perilous mission. He’s back in Colditz, and about to discover that Royce may have been involved in something far more sinister than trying to escape...

Guy says

I’ve always been fascinated by the story of Colditz Castle -- indeed I even wrote about it for my O-level history project –– and it was inevitable that I would set a thriller there. Naturally, I had to visit the castle itself, and the memory of cresting the brow of a hill on a wet November night to see the fang-like castle glowing in the distance will be indelible. Colditz is now being restored sympathetically, although there are those who maintain that the Saxon authorities are destroying much of the past. It is a hard balance to strike, as the building clearly needs maintaining, and indeed to make money. Nevertheless, much of the wartime atmosphere remains for the time being, so any Colditz nuts would be well advised to go as soon as possible. The details for a good guesthouse can be found here.

    Interestingly, Colditz means very little to most Germans, especially those from the former East Germany where the castle lies. For the Communists, the story of Oflag IVc did not fit in with the legend that all fascists were evil, as the camp authorities treated their prisoners relatively well. As Colditz was no death camp, its story was therefore covered up. I found a 1970s guide book to East Germany that made no mention of the town, let alone the castle.

       The biggest challenge with The Colditz Legacy was getting my characters to escape from the castle via a route that wasn’t well known. I’m sure that many readers will know the Pat Reid and Airey Neave books, and to have simply lifted something from them would have felt cheap. I hope my solution finds favour, especially from my fellow members of the Colditz Society!