
After finishing his rounds one June night, Watson receives a desperate visit from his wife's friend. Her husband has been absent for two days, and Watson goes into London's East End to bring him home. The search takes him to a riverside alley, where an unexpected meeting draws him into a much stranger disappearance.

Watson has finished his work as a doctor and is spending a quiet evening at home with his wife. A late caller may mean another journey into the night. When a distressed visitor arrives asking for help, Watson first listens to her story and then sets out to find the missing man.

As their cab travels toward Lee, Holmes explains the course of his investigation to Watson. The missing man is Neville St. Clair, a respectable married gentleman who lives outside London. The facts seem simple at first, yet Holmes cannot grasp a reliable clue, so Watson listens closely to the account of the disappearance.

By the time Holmes finishes his account, the cab has left central London and is approaching Lee. Neville St. Clair's whereabouts remain unknown. Holmes and Watson are heading for the family home, where Holmes has been staying during the inquiry. There they meet Mrs. St. Clair and examine the latest information together.

Morning light enters the guest room after Watson spends the night at the St. Clair home. Holmes appears not to have slept, remaining absorbed in the unanswered problem. While the household is still quiet, he and Watson prepare to leave early and test the conclusion that has taken shape during the night.