During the Cold War, ex-smuggler Harry Palmer is enrolled as a reluctant but talented spy; sent to Berlin, Harry embarks on a dangerous mission and his survival depends on his own wits and the interventions of Maddox.

Palmer embraces his intuition, but gun-for-hire Randall is always one step ahead; a tip-off from a key witness draws Jean and Palmer closer to the truth, but their discovery only opens the door to a mystery.

As they chase Randall to Beirut where he holds Dawson, Harry and Jean's relationship intensifies; suspicious Americans watch Dalby and find him in secret talks with a Russian spy; Colonel Stok offers Dalby a tempting trade.

Suspecting an American hand in Dawson's abduction, Dalby challenges General Cathcart by sending Harry and Jean to the neutron bomb test; Harry follows a trail of clues into big trouble; Maddox undermines Jean's trust in her colleague.

Harry is handed over to the Chinese military where he is subjected to a bewildering regime of mental torture; Dalby's love for Dr. Lavotchkin takes its toll on his better judgement.

Harry Palmer runs from the brainwashing but cannot hide from the agents of Cathcart's conspiracy; Jean discovers the origin of Maddox's conflict; Dalby learns his organization is to be axed; Harry worries about what has been planted in his mind.