Through a network known as the "Limbo Line", the KGB is kidnapping figures who have recently defected to the West and returning them to the Soviet Union for punishment. A British intelligence agent identifies the ballerina Irina Tovskia as the next victim, and sets out to rescue her in a mission that takes him from London, to Amsterdam and finally to Lübeck on the East German border. He is able to destroy the Limbo Line, but not prevent Irina being taken to Moscow.