In the story, a master criminal named Avery Knight takes on the challenge of predicting where a detective on a murder case will go to look for the murderer. He commits a random murder then tries to anticipate the moves of the great detective Shamrock Jolnes by reverse-engineering the detective's famous methods. When that approach fails, Knight decides to follow his own theory instead. The character of Shamrock Jolnes also appears in the short stories "The Adventures of Shamrock Jolnes" and "The Sleuths".