By the Pricking of My Thumbs

By the Pricking of My Thumbs is a mystery novel by the English writer Agatha Christie, first published in November 1968.

Tommy and Tuppence Beresford are the pair of amateur detectives Christie wrote about at intervals across her career, and in this book they are middle-aged, which is part of the joke: the visit to an aunt in a nursing home is the ordinary business of their lives rather than the beginning of an adventure. The resident who talks about something behind a fireplace and a poor child is Mrs Lancaster, and when the aunt dies and Mrs Lancaster is found to have gone the questions Tuppence has been half-ignoring become the case. The title comes from the witches' scene in Macbeth, and the novel is divided into four books as the search moves from the home to the village where Mrs Lancaster came from and into a part of her past that nobody in her family wanted to discuss.

Christie published more than sixty novels, and the Tommy and Tuppence books are among the few in which the detectives age with the series.