What is the name of Dr Watson’s wife in The Sign of the Four?

Dr Watson’s wife in The Sign of the Four is Mary Morstan.

Mary Morstan is introduced as a client who asks Sherlock Holmes to help investigate the mysterious annual delivery of a pearl. Her father, Captain Arthur Morstan, disappeared after returning from India, and the investigation eventually leads to the Agra treasure and the “sign of the four” pact.

Watson quickly develops romantic feelings for Mary, and the novel ends with their engagement. Their relationship is one of the clearest personal developments in the Holmes canon, although Doyle later mentions Watson’s marriages inconsistently. In several stories, Watson appears to be living with or assisting Holmes again, despite the earlier marriage.

Mary is sometimes confused with Irene Adler, Holmes’s celebrated opponent from “A Scandal in Bohemia.” Irene is a singer and adventurer who outwits Holmes, while Mary is a client and Watson’s wife. Mary’s later appearances are limited, and different adaptations vary considerably in how they portray her.