In Copenhagen in 1962, a high-ranking Soviet intelligence officer, Boris Kusenov (Per-Axel Arosenius), defects to the West. During debriefing, CIA agent Mike Nordstrom (John Forsythe) learns that Soviet missiles with nuclear warheads will be placed in Cuba.
Needing physical evidence, Nordstrom discloses Kusenov’s name to French agent André Devereaux (Frederick Stafford) and asks him to bribe Luis Uribe (Donald Randolph), a member of Cuba’s UN delegation, to provide photographs of documents that confirm the missile bases in Cuba. Devereaux decides to accompany his daughter, Michèle (Claude Jade), on her honeymoon to New York City with his son-in-law, François Picard (Michel Subor).
In New York City, a French-Martinican agent, Philippe Dubois (Roscoe Lee Browne), is to contact Uribe, who is the secretary to Cuban official Rico Parra (John Vernon), who is staying at the Hotel Theresa in Harlem to show solidarity with the black community.
Dubois sneaks into the hotel and bribes Uribe to take the documents from Parra’s office to photograph. Parra catches Dubois photographing the documents. Chased and shot at by Cuban revolutionaries, Dubois purposefully knocks into Devereaux, who is watching events from the other side of the street, and slips him the camera. A red-headed Cuban guard helps Devereaux to get up but lets him go. Dubois escapes into the crowd around the hotel.
Dubois’s photos confirm that the Soviets are placing missiles in Cuba. Devereaux, despite his wife’s accusations of infidelity, flies to Cuba. His mistress, Juanita de Cordoba (Karin Dor), was the widow of a “hero of the Revolution,” which enables her to work undercover in the resistance. Upon his arrival, Devereaux finds Parra, another of her lovers, leaving Juanita’s mansion. Devereaux asks Juanita to take photographs of the missiles. Juanita’s loyal domestic staff, Carlotta and Pablo Mendoza, pose as picnickers and photograph the missiles. Pursued, the two hide the incriminating film before they are captured.
During a mass rally and a lengthy speech by the líder máximo, the red-headed Cuban guard recognizes Devereaux’s face from the New York City incident.
Parra has heard from the tortured Carlotta Mendoza that Juanita is their leader. He embraces her and shoots her dead to save her from extreme torture.
At the Havana airport, the Cuban authorities fail to find the microfilms that Deveraux has. He returns to find that his wife has left him. Devereaux is to be recalled to Paris. Kusenov tells him about the existence of a Soviet spy organization, “Topaz,” within the French intelligence service. He is given the name of NATO official Henri Jarré (Philippe Noiret), who leaked documents to the KGB.
In Paris, he is picked up at the airport by his daughter and his son-in-law. Michèle brings to a cocktail Jacques Granville (Michel Piccoli), an old friend of André. Michèle hopes that her parents will get alon, but Nicole cannot forgive André’s affair with Juanita. André and Michèle stay alone, and Jacques complains the agent Martin (John van Dreelen) that Nicole married Andre.
Devereaux researches the leak and invites some of his old friends and colleagues, including Jarré, to a lunch at a fine Paris restaurant under the pretext of helping Devereaux prepare for his inquiry. Devereaux tells the others about Topaz to provoke some reaction. Jarré claims that it is misinformation and that Kusenov died a year ago.
Jarré starts to panic and visits the leader of the spy ring, Jacques Granville. Devereaux, Nicole, and Granville were close friends from their days together during the French Resistance. Granville tells Jarré that it was a mistake to say Kusenov was dead since the Americans will easily discover that Jarré lied. As Jarré leaves Granville’s house, Devereaux’s wife arrives to meet Granville, her lover.
Devereaux sends his son-in-law, François, to interview Jarré. Devereaux and Michèle rush to Jarré’s flat and find Jarré dead, which is a staged suicide, and François has disappeared. After being clubbed and kidnapped, François managed to escape from his captors’ car with an overheard phone number.
Nicole tells her family with tearful eyes that since the phone number is Granville’s, he must be the leader of Topaz. Granville, exposed, commits suicide (in the American and the French versions) or flees to the Soviet Union (in the British version).