: A woman turns to Sherlock Holmes who rents a room to a strange tenant. The detective finds out that the tenant hides his wife, from whom he fell in love, from a dangerous criminal.

Mrs. Warren speaks to Sherlock Holmes, renting a small apartment in her house. Ten days ago, a man came to her who agreed to rent an apartment for a fee twice as much as the hostess requested. The man spoke English correctly, albeit with an accent. He paid two weeks in advance, asked for his house key and demanded that he not be disturbed under any circumstances.

The tenant has been living in the house for ten days. I went out only once a day of arrival. He sits all day in his room, serves himself, walks back and forth. After his call, they leave him food under the door. If the tenant needs something, he writes a note in block letters. He asks for soap, matches, newspaper. Since Mrs. Warren’s husband is not at home all day, and she remains with the maid, both women tremble with fear.

The great detective studies the notes. Since they were written with errors, and the tenant speaks English correctly, Holmes concludes that another person lives in the room. He also studies newspaper ads requested by a mysterious tenant. Correspondence catches his eye, where it is reported that an apartment was rented in a house similar to Mrs. Warren's. A code is set between the correspondents.

Soon Mr. Warren is beaten in the street, and his wife associates this with the advent of a new tenant.

The great detective arrives at Mrs. Warren's house. Hiding, he sees a woman picking up a tray of food. Holmes concludes that the couple is afraid of something, and the man hid the woman so that even the landlady does not know who lives in her house.

In the evening, Holmes arrives at Mrs. Warren's house again. He sees someone in the house opposite giving signals with a candle. After counting the number of flashes of light and finding the corresponding letters, Holmes concludes that there are signals of danger. Suddenly the signals cease. Holmes rushes into the house opposite and in front of the entrance he meets a police inspector who also monitors the house, tracking down the criminal Giordano from the Scarlet Ring gang.

Entering the house, they see Giordano killed with a knife. Holmes gives a candle, and after a while a mysterious tenant arrives. She says that, being the daughter of a rich man, she married by love against the will of her father. They left for America. There, her husband met with Giordano, who had once dragged him into this organization. He wanted to get out of it, but that meant death. In addition, Giordano fell in love with a woman and began to pursue her. The couple left for London and hid, talking through the newspaper. Having met, the husband killed Giordano.

The inspector concludes that a woman's husband can only express gratitude.