In July 1945 MI6 agent Paul Dark took part in a top secret mission to hunt down and execute Nazi war criminals. Now it's 1969 and a KGB colonel called Slavin has walked into the High Commission with information indicating there is a double agent within the Service. Dark has been largely above suspicion during MI6's years of self-criminating but this time he's in the frame. His options are fight or flight - whatever the consequences.