The Adventure of the Red Circle - Sir Arthur Conan Doyle

Sherlock Holmes and Dr Watson come to the help of the landlady Mrs Warren. She has rented out a room to a man who has offered to pay twice the asking price, as long as she meets his requirements. The deal settled, the man left, only coming back when everyone was asleep. She leaves him meals and the daily paper on a chair by his door, where the lodger also leaves her a note if he needs anything. Since that first day she has not seen him."The Adventure of the Red Circle" is part of "His Last Bow".