The story begins when Hilton Cubitt of Ridling Thorpe Manor in Norfolk visits Sherlock Holmes and gives him a piece of paper with a mysterious sequence of stick figures.

Cubitt explains to Holmes and Dr. Watson that he has recently married an American woman named Elsie Patrick. Before the wedding, she had asked her husband-to-be never to ask about her past, as she had had some "very disagreeable associations" in her life, although she said that there was nothing that she was personally ashamed of. Their marriage had been a happy one until the messages began to arrive, first mailed from the United States and then appearing in the garden.

The messages had made Elsie very afraid but she did not explain the reasons for her fear, and Cubitt insisted on honouring his promise not to ask about Elsie's life in the United States. Holmes examines all of the occurrences of the dancing figures, and they provide him with an important clue—he realises that they form a substitution cipher and cracks the code by frequency analysis. The last of the messages causes Holmes to fear that the Cubitts are in immediate danger