: A young woman receives letters on which dancing people are painted. Sherlock Holmes discovers that notes are written by her ex-woman's fiancé, a Chicago gangster.

Mr. Hilton Kewbit, representative of the most ancient family in the English county of Norfolk, seeks help from Sherlock Holmes. A year ago, Mr. Kyuubit married a young American named Ilsey. Before the wedding, the girl took the word from him that he would never ask her about her past life. All this time the couple lived in love and harmony, but for some time something strange began to happen to Ilsi.

First, she received a letter from America, which she immediately burned. Soon, a drawing appeared on one of the windowsills, on which dancing people were depicted. Some of them were holding flags. The drawing was erased without giving any significance to it, but Ilsi found out about it and asked to be informed if such drawings still appear. Soon in the garden they found a leaf with the same figures. Seeing this, Ilsi lost consciousness. Since then, she lives in a dream, and her eyes are full of horror. Mr. Kyubit does not want to contact the police, as he is afraid that he will be ridiculed there. He cannot ask his wife either: a promise is a promise. It remains only to ask for help from the famous detective.

Sherlock Holmes agrees to help.He asks Mr. Kewbit to closely monitor the appearance of strangers in their area and carefully sketch out new dancing people.

Two weeks later, Mr. Kyubbit again visits the apartment on Baker Street. He is preoccupied and depressed. Drawings appear again and again, and Ilsi is melting before our eyes. One night, Mr. Kyubit decided to watch over the draftsman with a revolver in his hand, but his wife persuaded him to go to bed. Then he noticed how someone sat down under the door. Mr. Kyuubit wanted to catch a night visitor, but Ilsi did not allow, and in the morning he found a drawing on the door.

Sherlock Holmes begins to carefully study the drawings left to him by Mr. Kyubitom. After some time, a letter arrives from Norfolk with a new drawing, which alarms the detective. With the nearest train, he leaves for Mr. Kewbit’s house, but the tragedy has already occurred: Mr. Hilton Kewbit is killed, and his wife is seriously injured. According to the police, Mrs. Cuybit killed her husband, and then decided to commit suicide. The cook and the maid say the same thing: they were awakened by the sound of a shot, then they heard a second shot. Going downstairs, the women saw the dead master and his wounded wife lying nearby unconscious. The door windows were closed, and the room smelled of gunpowder.

Studying the room, Sherlock Holmes sees a bullet hole in her window frame and a handbag full of bank credit cards. Traces of men's shoes and a sleeve are visible under the window. The great detective pulls out sheets of drawings of dancing people from his pocket and plunges into work.He writes a note and asks for it to be handed over to a man named Ab Sleni, who lives on Elridge's farm. Meanwhile, Sherlock Holmes tells the police inspector about Mr. Cube’s visits and shows him the drawings. Dancing people are a code, and flags are used to mark the end of words. Gradually, the great detective unraveled this cipher and realized that the drawings were left by an American named Ab Sleni, who now lives on Elridge Farm. At first, Ab Sleen persuaded Ilsi about the meeting, then he began to threaten her. Upon request, Holmes found out that Ab Sleigh is one of Chicago's most dangerous bandits. Knowing the code, the detective wrote him a note on behalf of Ilsi.

The appeared American is sure that Mrs. Kyubit wrote the note, since no one knew the code except her. Upon learning that Ilsi was trying to commit suicide and is now in serious condition, Ab Sleen did not resist justice. Ilsi's father was the leader of the Chicago gang and came up with a code from the dancing men. Ab loved Ilsi and was supposed to marry her, but the girl did not want to have anything to do with the bandits and fled to England. Finding out where she was hiding, Ab began to pursue her. Ilsi begged to leave her alone, offered money, but Ab could not accept the loss of his beloved woman. During the conversation, her husband appeared and grabbed the revolver. Ab and Mr. Kyubit shot at the same time: Mr. Kuybit missed, and Aba shot was accurate. Seeing that a murder had occurred, the American ran away and returned only because he received an encrypted note.

Sherlock Holmes argues that Mr. Cubebit fired first. Considering this circumstance, the court replaces the death penalty with hard labor by Abu Sleni. Mrs. Kyubit is recovering and devoting her life to the care of the poor.