In the story, a man named Grant Munro seeks the help and advice of the famous consulting detective Sherlock Holmes. A cottage near to Grant Munro's home has recently become occupied. One of its two occupants is a Scottish woman who appears to be very unfriendly. The other is someone, Grant Munro does not know whether the person is a man or a woman, whose face appears to be unnaturally rigid and of an unusual color. On three occasions, Grant Munro's wife Effie goes to the cottage which is home to the unusual people. She refuses to tell her husband why she went there, telling him that it would be better if he did not know her reason. Holmes comes up with a theory that explains Effie Munro's behavior. His theory turns out to be completely wrong, although the mystery is solved anyway.