Germany 1941. It was the most incredible plan. No one gave them a chance. British officers Hugh Hartley and Malcom 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 friends behind.

London 1973. Hartley is a senior MI6 officer and a 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 on 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 …