Géo Paquet, called "The Gorilla", escapes from prison where he had been incarcerated, an imprisonnement intended to camouflage his real activities as agent n!1 of the French Information Service. Secret plans of the Military Air Force has disappeared. Géo suspects that one of his ex-agents had got them for a foreign embassy. But this agent is killed by the police during one of their raids. "The Gorilla" nevertheless manages to get the name of the chief of the spy network, and from then on sets out to unmask this character in spite of the fact that his is covered by diplomatic immunity. Thus he has to work alone, unknown to the police or the D.S.T. Caught after having tried to offer his services to "strangers", he escapes helpled by his wife, Chaboute. Tracked by the police, he manages to organise a general slaughter in which the spies are lead to kill each other off.