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.
Berlin in the 1960s is a city divided between Cold War lines with inhabitants of the Communist East trying to escape to the West. Even with the infamous Berlin Wall these escapes are common and successful.Colonel Stok (Oskar Homolka), the head of intelligence in Russia's Berlin section and the one responsible for preventing escapes over the Wall, contacts British Intelligence and informs them that he wants to defect to the West. British spy Harry Palmer (Michael Caine) is sent to West Berlin to find out if Stok's offer is genuine and arrange his escape. Palmer was once involved in black market dealings in Berlin and was given the choice of joining British Intelligence or going to jail. Returning to the city, he is re-united with his old associate, German national Johnny Vulkan (Paul Hubschmid), who also works for Palmer's superior Colonel Ross (Guy Doleman).Vulkan arranges for Palmer to go to East Berlin to meet Colonel Stok. In exchange for his co-operation with the British, Stok requests a meagre stipend, a house in the country and his escape must be carried out by Kreutzmann (Günter Meisner), a Berlin gangster responsible for the most successful escapes. Stok claims that Kreutzmann's escapes have lead his department to be investigated and that he must get out before things turn nasty.Returning to West Berlin, Palmer is picked up by a beautiful young woman called Samantha Steel (Eva Renzi), who invites him to a party but instead takes him to her flat for drinks, dinner and presumably more as Palmer is next seen leaving her place in the morning. Not taken in by Samantha's charms, Palmer hires a burglar to search her apartment to figure out who she really is. The thief discovers a number of passports of various nationalities under different variations of her name and a little black book in her safe which lists names of men next to million-dollar figures. Returning to his hotel room, Palmer finds that it too has been ransacked.Palmer negotiates an arrangement with Kreutzmann without revealing the details of the one whom the British want to get across the Wall. As part of his payment, Kreutzmann demands a set of identity papers.Palmer tests Stok in order to determine how sincere he is about defecting. The test seems conclusive and Palmer returns to London. From Hallam (Hugh Burden), the documents manager back at MI5, Palmer receives documents in the name of Paul Louis Broum. As he places the envelope in his briefcase for return to Berlin, he notices the same name on the photocopy of Samantha's little black book, with the figure $2,000,000 next to it.Palmer returns to Samantha and makes a point of letting her see the envelope with Broum's name. Dropping all pretence, she admits that she is an Israeli agent. Broum is a Nazi war criminal who stole millions from the Jews during the war and hid it in a Swiss bank account. The Israelis need the papers in order to reclaim the money. Although she threatens to kill him, Palmer refuses to give her the documents since he needs them to pay Kreutzmann.Kreutzmann and his men murder an elderly East Berliner whose body is claimed by a relative in the West – actually someone employed by Kreutzmann. A body transfer is arranged but as the hearse makes its way from the morgue to the checkpoint, it is hijacked by Kreutzmann's men and replaced with another which contains a different coffin.The coffin is taken to West Berlin and delivered to an abandoned warehouse where Palmer and his associate Vulkan are waiting. But when the coffin in opened it is found to contain the dead body of Kreutzmann! Stok's whole defection was simply a bluff to lure Kreutzmann out and put an end to the escapes he so brilliantly organised. Although well informed, he and his men never knew in advance that Stok was the intended client.Before Palmer can get away from Kreutzmann's outraged accomplices, he is knocked unconscious by Vulkan who gets hold of the Broum documents only to be held up by Samantha and two other Israeli agents who take away the papers.Vulkan tells Palmer that he was knocked out by another of Kreutzmann's men. They then go to a safe house where British officials are waiting to debrief Stok. Stok of course is not there, meaning that a lot of valuable time and money has been wasted. Palmer's boss, Colonel Ross, is also present and Palmer tells him about the Broum documents. Ross was unaware that they were being used as part of the deal with Kreutzmann. He then reveals to Palmer that towards the end of the war, Paul Louis Broum, a guard at a concentration camp, murdered a resistance fighter called Johnny Vulkan and assumed his identity. Ross got hold of the documents and used them to blackmail Broum into working for him.Now that the documents are missing, Ross has nothing with which to keep a hold on Broum/Vulkan and cannot risk him defecting. He therefore orders Palmer to kill Broum. Palmer won't kill anyone in cold blood and allows Broum/Vulkan to get away.Back in West Berlin, Palmer meets Stok who is over for a routine meeting with his Western counterparts. The affable Russian confirms that his supposed defection was just a trap to get rid of Kreutzmann. He and Palmer even joke about the latter himself defecting to the East; Stok advises: "If you need to get out in a hurry, ask Vulkan. He knows the way."Meanwhile, Broum/Vulkan goes to Samantha's flat, murders an Israeli agent and gets the documents back. He then meets Hallam, the Intelligence official who gave Palmer the Broum documents in London. However, the documents that they now have are in fact forgeries made by one of Palmer's underworld Berlin contacts. Hallam goes to Palmer, saying that he has been sent by Ross to get the real documents back. Palmer never believed Hallam's claim that he selected the Broum documents at random and forces him to admit that he is in league with Broum: they took advantage of the situation to get the documents out of London and now intend to use them in order to claim the Nazi loot that Broum deposited in the Swiss banks.Palmer and Hallam go to a quiet part of the Berlin wall through which Broum and Hallam intend to slip into the East and thus to Switzerland, but Broum kills Hallam and makes away with the documents. However he is subsequently killed by the Israeli agents who were tailing Palmer. Palmer lets them take the genuine Broum documents.When Vulkan's body is discovered, Ross is satisfied that he will just be another martyr shot while escaping to the West. Palmer however turns down Ross's offer of a bonus for his work and leaves.By the time of the next film, Billion Dollar Brain (1967), Palmer has resigned from British Intelligence.