After recovering the famous Borgia pearl from shipboard thieves, Sherlock Holmes is held responsible for its theft. While visiting the museum where it goes on display, Holmes shows the curator how easily it could be stolen by simply cutting the electrical wires. During that demonstration, Giles Conover, a well-known thief, snatches the pearl and runs off. He's soon caught but the pearl is nowhere to be found. Soon after, homes are being broken into with the occupants having their backs broken. There also seems to be a large amount of china broken in the process. After several such break-ins, Holmes realizes that several similar pieces of porcelain, all of a bust of Napoleon, are found at each house. Realizing its significance, he sets a trap for the thief.