At the end of his magic show at the Tivoli theater, Chatrand the Great announces over a radio broadcast that he is trying to establish the identity of a victim of amnesia, his assistant who goes by the name of Alexander. Found unconscious with a head wound two years earlier in the streets of Washington, Alexander, now a mind reader in the act, cannot remember anything about his previous life. Beverly Lane, whose brother Paul disappeared two years earlier, listens intently to her radio, but her uncle, financier John Carrington, calls the announcement a cheap publicity stunt. When Beverly insists on going to the theater, Carrington accompanies her. Before his performance, Chatrand, upon seeing Beverly through the stage curtains, recognizes her from a picture in the locket Alexander carries. He has always wanted to meet the woman in the picture. During the act, Chatrand blindfolds Alexander and has him describe objects belonging to members of the audience and answer their questions. When Chatrand asks Alexander to describe Beverly's locket, which is identical to Alexander's, Carrington protests and struggles with Chatrand. Sonya, Chatrand's assistant, pulls a light switch. In the dark, a hand wearing a spider ring fires a gun, and Carrington falls. The police soon arrive and keep the audience from leaving, as a man from the audience, Dr. Blackstone, attends to Carrington. After Inspector Riley finds a gun beside Alexander, who is unconscious, Chatrand removes Alexander's mask. Beverly then embraces him and identifies him as her lost brother. Chatrand brings Alexander out of his trance, and upon seeing Beverly, Alexander exclaims, "He tried to kill me; I had to do it!" Treating this as a confession, Riley has Alexander and Beverly taken to the theater manager's office, while he keeps Chatrand under observation. Chatrand, however, escapes into a casket and then through a trap door. Alexander tells Beverly that two years earlier Carrington attempted to steal all their money, and that when Carrington tried to kill him, he fell, precipitating his amnesia. Chatrand then finds out that Carrington had been receiving telephone calls from someone who lost a great deal of money to him. When Riley learns that Carrington has died, he arrests Alexander for first-degree murder. Chatrand, however, convinces Riley to let him conduct a seance before the audience is allowed to leave to try to make the murderer betray himself. During the seance, as Chatrand's image appears before the audience, and Carrington, speaking through Chatrand, threatens to name his murderer, a shot breaks the mirror which is conveying the image. Chatrand next has Alexander, in the guise of a mind reader, attempt to "find" the mind of the murderer. After he reveals a number of dark secrets in the minds of some members of the audience, Alexander says that the murderer wears a spider ring, and he names the row in which the murderer is sitting. As he is about to reveal the murderer's seat number, a shot rings out. Dr. Blackstone, who hysterically says that Carrington deserved death for ruining a savings bank and turning his family and thousands of others into paupers, is apprehended. Chatrand, who suffered a wound to his arm, is attended to by Beverly, who has grown fond of him.