Mr. Jabez Wilson, a struggling London pawnbroker with brilliant red hair, is hired by the mysterious Red-Headed League for a high-paying, nominal job: copying the Encyclopædia Britannica in an empty office for four hours a day. When the league abruptly dissolves after eight weeks, Wilson seeks the help of Sherlock Holmes, bewildered by the sudden loss of his income.
Holmes investigates the pawnbroker's shop and his clever, underpaid assistant, Vincent Spaulding, noting suspicious details about the assistant's trousers and his frequent disappearances into the cellar. Convinced that a major crime is being planned, Holmes enlists Scotland Yard and a bank director to stake out the deep vaults of a nearby city bank on a Saturday night.
Waiting in total darkness, the men are soon rewarded when the flagstones of the vault floor are lifted from underneath. Two notorious criminals emerge into the gold-storage cellar through a tunnel ingeniously excavated from the pawnbroker's basement.
Holmes and the police spring their trap, capturing the mastermind of the underground plot red-handed. The elaborate scheme of the Red-Headed League is revealed as a brilliant diversion to keep the pawnbroker out of the building during business hours while the tunnel was completed.
