Despite the warning uttered by Blake, the house detective of the Alhambra, Mrs. Cluett refuses to deposit her gems in the hotel vault for safe keeping, A few nights later, a mysterious thief enters the woman's apartment, binds and gags her and then departs with the gems. When Mrs. Cluett's maid discovers her mistress's plight the following morning. Blake is summoned. The man finds a black robe, similar to that worn by the thief, in the maid's room. Mrs. Cluett, however, declines to have the girl arrested. The woman announces that the gems stolen by the intruder were paste imitations and reveals the fact that the real gems were in an old shoe. Although Blake expresses the desire to handle the case by himself, Mrs. Cluett secures the aid of Bertha and Talcott. Bertha becomes Mrs. Cluett's maid, while Talcott poses as a wealthy guest. Confident that the crook will appear a second time, the detectives set a trap for him. Again the black-robed intruder appears. Bertha is ready for him. A howl of pain informs her that his hand is caught in the heavy spring trap concealed in a clothes closet. When Bertha endeavors to arrest him, however, the man dashes out of the room. He finds Talcott waiting. A sudden blow sends Bertha's assistant reeling. The thief dashes upstairs and escapes. Accompanied by the hotel manager, Bertha and Talcott visit Blake in his room on the top floor. The man's bandaged hand arouses the detectives' suspicions. They speedily unmask him as the real thief. The gems he had just stolen are recovered and the house detective is led away under arrest.