The story is set in 1947, following a long-retired Holmes living in a Sussex village with his housekeeper and rising detective son. But then he finds himself haunted by an unsolved 50-year old case. Holmes' memory isn't what it used to be, so he only remembers fragments of the case: a confrontation with an angry husband, a secret bond with his beautiful but unstable wife.
An aged, retired Sherlock Holmes deals with dementia, as he tries to remember his final case, and a mysterious woman, whose memory haunts him. He also befriends a fan, the young son of his housekeeper, who wants him to work again.