One evening in June 1889, while Watson is getting ready for bed, a school friend of his wife’s calls on the family. Her husband is an opium addict and has been gone for several days. She is afraid for him but does not want to go alone to the opium den he frequents. Watson volunteers to go and fetch her husband.

While at the opium den, Watson encounters Holmes in disguise and the detective asks him to help him investigate an unusual case. Watson quickly takes care of his acquaintance and joins the detective in his work.

A gentleman, Neville St. Claire, has been missing, presumed dead, for a week. He was last seen by his wife outside the opium den. When she could not enter the building, she called the police, who then searched the premises and found St. Claire’s clothes as well as some blood next to an open window overlooking the wharf behind the building. They assumed the man was murdered and thrown into the water. The only occupant of the apartment was a beggar who was immediately arrested.

St. Claire’s wife hires Holmes to investigate her husband’s disappearance as she does not believe he is dead. She shows them a letter that was undoubtedly written by her husband telling her he is alive and will return soon.