During the Cold War, ex-smuggler Harry Palmer is enrolled as a reluctant but talented spy. Harry embarks on a dangerous undercover mission in Berlin.

Under the diligent eyes of agent Jean, Palmer's intuition edges them closer to the professor while gun-for-hire former MI6 man 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 more chilling mystery.

Harry and Jean arrive in Beirut in hot pursuit of Randall, who is holding Professor Dawson. Meanwhile, Dalby holds a secret rendezvous with Stok, a Russian colonel.