Inspector Alan Grant of Scotland Yard is laid up in hospital with a broken leg. The novels he tries reading to pass the time all bore him, until a real-life mystery awakens his curiosity and soon turns into an obsession. Studying a portrait of the notorious Richard III he finds himself wondering whether such a man could really have been the ogre of legend, who murdered his own nephews in his greed for power. Enlisting the help of an American scholar, Inspector Grant is determined to get to the bottom of the mystery of the Princes in the Tower once and for all.