Hercule Poirot investigates a group of wealthy ladies, a proclaimed revolutionary, an Austrian doctor, and a newly married Linnet Ridgeway with her husband Simon Doyle who are also joined by her uncle.They are all intertwined in some way, but most of them are Linnet's enemies. Her biggest enemy seems to be her closest friend Jacqueline de Bellefort (Mia Farrow), who dated Simon (Simon MacCorkindale) before he decided to marry Linnet.
Poirot's role is played by Peter Ustinov, who just like David Suchet in the television version of this book is also slightly chubby, with a sense of humour as well as the pride of his Belgian heritage. In its TV version, the story begins with a romance between Jacqueline de Bellefort and Simon Doyle, while the film provides more introduction into the opulent life Linnet (Lois Chiles) led before meeting Jackie's boyfriend, Simon.
Jacqueline is severely hurt by Linnet's betrayal. She follows the newly married couple everywhere, mocking them. In the end, Linnet and her husband hope to escape her by going on a trip along the Nile, but Jacqueline traces them also there. The atmosphere on the ship intensifies all the more that Jacqueline expresses openly her hatred towards Linette, revealing that she has a small pistol that she wouldn't mind using.
Linnet has lived the life of luxury without consideration for anyone else. Her wealth has been the subject of envy of those she knew. Everybody has a reason to hate her and she is aware of it. She caused bankruptcy, various downfalls and sued for defamation. Her maid, Louise Bourget (Jane Birkin) is not allowed to marry an Egyptian man, as Linnet denies her dowry, deciding also that he is not appropriate for her. The romantic surroundings of the river Nile unveil conflicts and passions that come to the surface as crimes of passion as well.
Guests on the ship include writer Salome Otterbourne played by Angela Lansbury. Other great performance involves Maggie Smith and Bette Davis as Miss Bowers and Miss Van Shuyler, Jack Warden as Dr Bessner, and Jon Finch as Jim Ferguson.
Poirot becomes concerned when a large stone falls down only just missing Linette and Simon when they explore an on-shore temple. One day, when a group of passengers play cards, Jackie displays another jealous rage during which she shoots Simon in the leg. That night Linnet is also killed. The most obvious suspect, Jackie has been watched all night by Ms Bowers. She becomes the only person on the ship who could not commit this crime. The pistol that is thought to have killed Linnet is recovered from the river along with Mrs van Shuyler's stole.
When more murders are committed on the steamer, various mistakes to hide them are made, helping Poirot to unravel the mystery. After Louise, Linnet's maid is also found dead, Poirot eventually discovers who is behind all the murders. He realizes that the murders that follow are to hide any revelations about who killed Linnet. They are also to hide the plot designed by Jackie and Simon to acquire Linnet's fortune by arranging for Simon to marry her and then kill. When they both admit it, Jackie decides to sacrifice herself killing her boyfriend and then herself, as she is unable to free herself from her love for Simon.