An American family - Dr. Benjamin "Ben" McKenna, his wife, popular singer Josephine "Jo" Conway McKenna, and their son Henry "Hank" McKenna - are vacationing in French Morocco. Traveling from Casablanca to Marrakesh, they meet Frenchman Louis Bernard. He seems friendly, but Jo is suspicious of his many questions and evasive answers.Bernard offers to take the McKennas to dinner, but cancels when a suspicious-looking man knocks at the McKennas' hotel-room door. At a restaurant, the McKennas meet friendly English couple Lucy and Edward Drayton. The McKennas are surprised to see Bernard arrive and sit elsewhere, apparently ignoring them.The next day, attending a Moroccan market with the Draytons, the McKennas see a man chased by police. After being stabbed in the back, the man approaches Ben, who discovers he is Bernard in disguise. The dying Bernard whispers that a foreign statesman will be assassinated in London and that Ben must tell the authorities about "Ambrose Chappell". Lucy returns Hank to the hotel while Ben, Jo and Edward go to a police station for questioning about Bernard's death. An officer explains that Bernard was a French Intelligence agent.Ben receives a threatening telephone call at the police station; Hank was kidnapped but will not be harmed if the McKennas say nothing to the police about Bernard's warning. Knowing Hank was left in Lucy's care, Ben dispatches Edward to locate him. When Ben and Jo return to the hotel, they discover Edward checked out. Ben realizes the Draytons are the couple Bernard was looking for and are involved in Hank's abduction. When he learns the Draytons are from London, he decides he and Jo should go to London and try to find them through Ambrose Chappell.In London, Scotland Yard's Inspector Buchanan tells Jo and Ben that Bernard was in Morocco to uncover an assassination plot; they should contact him if they hear from the kidnappers. Leaving Jo and her friends in their hotel suite, Ben searches for a person named Ambrose Chappell. Jo realizes that "Ambrose Chapel" is a place, and the McKennas arrive at the chapel to find Edward leading a service. Jo leaves the chapel to call the police. After Edward sends his parishioners home, Ben confronts him and is knocked out and locked inside. Jo arrives with police, but they cannot enter without a warrant.Jo learns that Buchanan has gone to a concert at Royal Albert Hall, and asks the police to take her there. Once the police and Jo leave, the Draytons take Hank to a foreign embassy. In the hall's lobby, Jo sees the man who came to her door in Morocco. When he threatens to harm Hank if she interferes, she realizes he is the assassin sent to kill the foreign prime minister.Ben escapes the chapel through its bell tower and reaches the hall, where Jo points out the assassin. Ben searches the balcony boxes for the killer, who is waiting for a cymbal crash to mask his gunshot. Just before the cymbals crash, Jo screams and the assassin misses his mark, only wounding his target. Ben struggles with the would-be killer, who falls to his death.Through a spy in the embassy, the police find out the Draytons are there and conclude that Hank is likely to be with them, but that it is sovereign and exempt from an investigation. The McKennas, desperate to find Hank, secure an invitation from the grateful prime minister. In a dialogue with Edward, the ambassador reveals that he organized the plot to kill the prime minister and blames the failed attempt on the Draytons. Knowing that Hank can testify against them, he orders the Draytons to kill the boy.The prime minister asks Jo to sing. She loudly performs "Que Sera, Sera (Whatever Will Be, Will Be)", so that Hank will hear her.