Germany 1941 British officers Hugh Hartley and Malcolm Royce are imprisoned in the infamous Colditz prison. Mounting an escape, they reach the Swiss border but, as they are about to find freedom, Royce is shot and Hartley is left to cross the border alone. London 1973 Now a senior officer with MI6, Hartley comes across intelligence that convinces him Royce is still alive and being held in Colditz