A group of con artists stake their claim on a bogus uranium mine.

In a small Italian port, as the four businessmen, Petersen, Julius O'Hara, Maj. Jack Ross and Ravello, whom Billy Dannreuther has been representing in a scheme to acquire uranium-rich land in British East Africa, are led away by police officers, Billy relates how they came to be arrested: Six months earlier, Billy, an American, his Italian wife Maria and his business associates are about to board a tramp steamer to Africa, where Billy has a contact who will arrange for the group to benefit at a land auction. The ship, however, develops engine trouble and the group's departure is delayed. While they wait, Billy encounters an apparently upper-crust, proper, English couple, Harry and Gwendolen Chelm, who are traveling on the same ship to take over a coffee plantation Harry has inherited. The eccentric Gwendolen, who lies about their background and has a vivid imagination, tells Billy that he and his associates are very mysterious and that she suspects they are evil doctors, bound for the heart of the jungle to perform experiments on the natives. Later, Billy meets with Petersen and the others, who are concerned that Billy's friend may make another deal when they do not arrive on time. After accusing Ross of the London murder of a British Colonial officer who was part of their plan, Billy reassures them his friend will not let them down. When Billy and Maria take the Chelms to dinner, Billy reveals he has extensive personal knowledge of the area. The next day, Harry has a cold, so Billy invites Gwendolen to visit a villa he once owned and experiences more of her fanciful notions when she claims he is making a pass at her. After overhearing Gwendolen tell Billy that the plantation Harry is inheriting is rich in uranium deposits, O'Hara informs the others. Meanwhile Maria, an Anglophile, brings the ailing Harry afternoon tea and later tells Billy that she is interested in the Englishman. Soon O'Hara, on behalf of the group, expresses his concern that Billy may not be entirely committed to them and, despite Billy's reassurances, Petersen tells Billy that they both will now fly to Africa to protect their interests. Although Billy points out that the auction is two weeks away and their early arrival might be considered suspicious, Petersen insists and he and Billy leave in an old taxi for the nearest airport. En route, the taxi breaks down and when they push it, they accidentally launch it over a cliff into the sea. After Harry learns that Billy and Petersen are presumed to have died in the accident, he breaks the news to both Maria and Gwendolen. The money Petersen was carrying in a suitcase was also lost, so Ravello tries to raise new capital by explaining their scheme to Harry. Just then, to everyone's surprise, Billy and Petersen return to the port and the purser announces that the ship is finally ready to sail. Gwendolen informs Billy that she has told her husband that she is in love with him and wants Billy to go away with her. When Billy refuses, they both board the ship. Soon after, Petersen receives a cable from a colleague in London who has investigated the Chelms and states that they are not the rich, landed gentry Gwendolen has claimed them to be. Later, after Gwendolen confesses the same to Billy, Harry states that he learned from Ravello that they are a gang of crooks about to swindle a country out of its uranium deposits and that he intends to report them to the authorities. The ship's engine breaks down again and Harry, an ex-Royal Marines officer, attempts to fix it but, after a further explosion, the captain blames Harry and takes him prisoner. Billy, concerned that his associates will murder Harry to silence him, warns Gwendolen that they have already killed a man in London, and together they manage to thwart an attempt on Harry's life. Later, when informed that the ship is sinking, Billy goes to free Harry, but discovers that he has escaped, leaving behind a note saying that he hopes to swim to shore. All the other passengers, including Maria and Gwendolen, jump into a lifeboat and eventually land on a sandy beach, where they are arrested by Arab horsemen. After they are interrogated by Ahmed, an Arab official who suspects that they may be spies or revolutionaries, Ahmed surprises Billy by asking him about film star Rita Hayworth. Capitalizing on Ahmed's obsession with Miss Hayworth, Billy persuades him to release them in exchange for a large bribe and a promise to arrange an introduction to Rita. The group then returns in a small boat to the Italian port from which they sailed and are met by an inspector from Scotland Yard, who is investigating the Colonial officer's murder. When it appears that the inspector believes their various stories, Gwendolen takes it upon herself to implicate everyone except Billy in the London murder and in the attempt on her husband's life. After the four are taken into custody, Gwendolen receives a telegram from British East Africa and shows it to Billy, who bursts into laughter when he reads that Harry has acquired the land Petersen and the others had attempted to steal and that he expects to become rich from the uranium. Harry also writes that he is willing to overlook Gwendolen's extraordinary behavior and asks her to join him.