Holmes received a letter from Professor Charles Hardcastle, in which he begged him to pay him a visit. He suspects that someone breaks into his house from time to time and, to quote the professor, “seeks to cause monstrous damage to the house.” At first, Holmes considered the incident to be one of many ordinary incidents and, being completely absorbed in the investigation described in the story “Identification,” did not wanted to delve into it. However, new facts soon came to light, upon reflection on which Holmes realized that this was an extremely unusual case. The story sheds light on a blind spot in the life and exploits of Sherlock Holmes and worthy complements the classic series of adventures of the Great Detective.