In 1947, Sherlock Holmes, long retired, lives in a sleepy Sussex village with his housekeeper, Mrs Munro, and her amateur-sleuthing son, Roger. But far from living out a peaceful retirement, he is haunted by an unsolved case from fifty years ago. He remembers only fragments: a confrontation with an angry husband, a secret bond with his beautiful but unstable wife. With his legendary mental powers on the wane, and without his old sidekick Watson, Holmes is faced with the toughest case of his life — a case that might finally reveal to him the mysteries of the human heart.