Mary Morstan became the wife of Dr. John Watson. Sherlock Holmes said that Mary Morstan might have been most useful in detective work if she had only remained single. She - had a decided genius - that way.First appearing in 'The Sign of Four' and after the case is solved Watson proposes to her and they marry in 1889. She probably died before The Adventure of the Empty House where Doctor Watson writes, In some manner he had learned of my own sad bereavement .