Mary Morstan, the wife of Dr. Watson, is one of the main characters in the Sherlock Holmes canon. She is first introduced in The Sign of Four, where she and Dr. Watson tentatively become attracted to each other, but only when the case is resolved is he able to propose to her. She is described as blond with pale skin. At the time she hires Holmes she had been making a living as a governess. Although at the end of the story the main treasure is lost, she has received 6 pearls and will probably receive 6 more pearls and a chaplet of the Agra Treasure.


Although it was "love at first sight", Mary Morstan and Dr. Watson's marriage fluctuates somewhat. In The Adventure of the Crooked Man, Watson goes off with Holmes to solve a locked room mystery the summer after his marriage. She is concerned enough about his health to send him to the country during "The Boscombe Valley Mystery", but when Mary Morstan dies (the circumstances of which are not related in the Sherlock Holmes canon), Watson moves back in with Holmes and makes no reference to the loss, though it is speculated that he married again, which raises questions as to how close they actually were. It is probable that Mary Morstan died in the interim between "The Adventure of the Final Problem" and "The Adventure of the Empty House", given that in his farewell letter to Watson, Holmes asks his old friend to "give my regards to Mrs. Watson"; upon Holmes' return, Watson writes, "In some manner he had learned of my own sad bereavement"; and in "The Adventure of the Norwood Builder", one of the most immediate adventures after Holmes' return, Watson has returned to the old quarters in Baker Street.