The Daughter of Time [Inspector Alan Grant #5]

In 1990, The Daughter of Time was selected by the British Crime Writers' Association as the greatest mystery novel of all time. Alan Grant, Scotland Yard Inspector (a character who also appears in five other novels by the same author) is feeling bored while confined to bed in hospital with a broken leg. Marta Hallard, an actress friend of his, suggests that he should amuse himself by researching a historical mystery. She brings him some pictures of historical characters, aware of Grant's interest in human faces. He becomes intrigued by a portrait of King Richard III. He prides himself on being able to read a person's character from his appearance, and King Richard seems to him a gentle and kind and wise man. Why is everyone so sure that he was a cruel murderer?