At the beginning of MR. MOTO'S LAST WARNING, a man claiming to be a world famous detective, Mr. Moto (Peter Lorre) of the International Police, is abducted and murdered. The murder takes place soon after the supposed Mr. Moto gets off a ship at Port Said in Egypt.In fact the real Mr. Moto is already in Port Said, investigating a conspiracy against the British and French governments. The murdered man was Mr. Moto's colleague, impersonating him to mislead the conspirators-a Frenchman named Fabian (Ricardo Cortez) and an Englishman named Eric Norvel (George Sanders)-who are working for an unnamed foreign power.After his partner's murder, Mr. Moto will stop at nothing to foil the plot of the conspirators. Along with a British Secret Service agent, Danforth (John Carradine), Mr. Moto discovers that the saboteurs have placed mines in the Suez Canal harbor in preparation for the arrival of the French fleet. Their twisted aim is to make the British look responsible for the destruction of the French fleet, and thus foment a war between France and Britain.