 The man who knows too much is American doctor Ben McKenna. On holiday in Morocco with his wife Jo and his eight-year-old son Hank, he inadvertently witnesses a murder in a market and becomes privy to a plot of political assassination. This being masterminded by the Draytons, an English couple they have met in a restaurant, and is due to take place in London in a few days  time. In order to prevent McKenna from going to the police, the couple kidnap Hank. Ben is warned not to tell the police what he knows. Hank s life depends on his silence.