The story begins with Sherlock Holmes and Dr. Watson taking a boat trip down the River Thames. They stop at Eel Pie Island, a small island in the middle of the river, home to a number of artists and bohemians. Holmes and Watson go to the island's only pub, the Eel Pie House where they are greeted by the landlord, Mr. Jones. He tells them that a young man named John Smith has been found dead in his room, with a bottle of poisoned rum beside him. Holmes and Watson investigate the crime scene, finding a number of clues, including a footprint and a piece of paper with a strange message on it...