Sly and dry intelligence agent Harry Palmer is tasked with investigating British Intelligence security, and is soon enmeshed in a world of double-dealing, kidnap and murder when he finds a traitor operating at the heart of the secret service.

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.

A former British spy stumbles into in a plot to overthrow Communism with the help of a supercomputer. But who is working for whom?

Harry Palmer heads a private investigation business based in Moscow. His associates are Nikolai "Nick" Petrov, ex-CIA agent Craig, and ex-KGB Colonel Gradsky. They take on the job of finding 1000 grams of weapons-grade plutonium stolen from the Russian government, though they do not know the identity of their client.