Colonel Stok, a Soviet intelligence officer responsible for security at the Berlin Wall, appears to want to defect but the evidence is contradictory. Stok wants the British to handle his defection and asks for one of their agents, Harry Palmer, to smuggle him out of East Germany.

Harry Palmer, coerced into becoming a British spy, is sent to Berlin by Colonel Ross of Intelligence to arrange for the defection of Colonel Stok, the Soviet officer in charge of Berlin Wall security. The old Russian demands a foolproof method of escape, and Palmer contacts Johnny Vulkan, a fellow agent and former black market colleague who puts him in touch with Kreutzmann, a sinister professional escape artist. At the same time Palmer becomes involved with model Samantha Steel, an Israeli agent engaged in hunting Nazi war criminal Paul Louis Broum. Broum possesses documents which tell of a fortune stolen from Jews by Nazis during World War II and hidden in a Swiss bank account. Kreutzmann's plan is to arrange a funeral, hide Stok in a coffin supposedly belonging to an East German, and send it across the border. All goes as scheduled, but when the casket is opened in West Berlin, it contains the murdered body of Kreutzmann. Soon Palmer discovers that he has been double-crossed by everyone involved in the operation: the documents given to him by Ross to aid Kreutzmann are the very documents sought by Samantha's Israeli organization; Vulkan is really Broum; and Stok contrived the entire defection hoax to eliminate Kreutzmann, who posed a threat to his security arrangements. Vulkan corners Palmer in an abandoned building and forces him to hand over the documents. To protect himself from Samantha, who believes the documents are still in his possession and would kill him to obtain them, Palmer tricks Vulkan into switching topcoats. As the ex-Nazi leaves the building in Palmer's trenchcoat, the Israelis open fire. Palmer points out the documents in the dead man's pocket and strolls off.