Betrayed by his manager, a master magician uses his skills to seek revenge.

In the late 1800s, magician and inventor Don Gallico prepares the opening of his new show in which, as Gallico the Great, he will present his dangerous new act, wielding a buzz-saw that gives the illusion of severing the head of his assistant, Karen Lee. That evening Gallico performs part of his act disguised as his rival, The Great Rinaldi, and is a success with the audience. The introduction of the buzz-saw routine is interrupted and the show halted, however, by the arrival of businessman Ross Ormond and the police with an injunction against Gallico. Although outraged, Gallico admits to Karen's beau, detective Lt. Alan Bruce, that he has a contract with Ormond, who runs Illusions, Inc., a company that provides magicians' tricks. Later, back at the Illusions, Inc. warehouse, Alan informs Gallico that the contract with Ormond is legally binding and gives Ormond anything Gallico should invent. After Alan departs, Ormond and his partner Rinaldi arrive to examine the buzz-saw, and Ormond gives the apparatus to Rinaldi for his show, infuriating Gallico. Later, when they are alone, Ormond chides Gallico for his resentment, pointing out that he provided Gallico the opportunity to invent. Gallico assails Ormond for stealing his wife Claire long ago, and when Ormond responds blithely, Gallico becomes outraged and attacks him, decapitating him with the buzz-saw. Gallico hides the body and makes a mask from Ormond's head. Later, Gallico learns from Karen and Alan about a local university pep-rally bonfire scheduled for that evening. Disguising himself as Ormond with the new mask he has created, Gallico makes Ormond's body look like a stuffed dummy and attends the bonfire, where he places the "effigy" figure atop the burning pyre. The next day, still disguised as Ormond, Gallico, calling himself Ward Jamison, takes a room at the home of Frank Prentiss and his mystery-writer wife, Alice. A few days later at the workshop, Gallico receives a visit from Claire, who although now separated from Ormond, is curious about his whereabouts. Gallico declares that he has no knowledge of Ormond's location, so Claire reports her husband missing to the local police. Spotting the announcement and photo of Ormond in the newspaper, Alice summons Claire and reveals her suspicion that "Jamison" is Ormond. When "Jamison" returns to his room that evening, he finds Claire, but under the lights, she realizes that he is not her husband. She snatches the mask from Gallico's face and he admits to having murdered Ormond. Claire remains unconcerned, however, declaring that she only wanted Ormond's money. When she suggests getting back together with Gallico, he is overcome with rage and strangles her. Alice and Frank hear Claire's screams and break into the room, but find "Jamison" has fled through the window. At the inquest for Claire's murder, Gallico, Karen, Rinaldi and the Prentisses are questioned and Ormond is declared the official suspect. Some weeks later, Gallico invites Alice and Frank to witness the unveiling of his latest device, a crematorium. Rinaldi sneaks in to see the successful demonstration, which Gallico runs with Karen. After Karen and the Prentisses depart, Rinaldi appears and claims the crematorium, as Ormond's partner. Gallico refuses, but Rinaldi divulges his belief that Gallico has killed Ormond and the price for his silence is having exclusive rights to Gallico's inventions. Gallico locks Rinaldi into the studio and murders him in the crematorium, then takes over Rinaldi's act, disguised as his famous rival. When Alan arrives one evening and explains his interest in a new criminal identification procedure involving fingerprints, "Rinaldi" feigns outrage that he should be a suspect and avoids the process. Later, however, Alan returns to Rinaldi's dressing room and gets prints. Alan discovers that Ormond's prints from the shop and those from Rinaldi's dressing room are the same, but the police chief is dubious of the new method and refuses to allow Alan to continue. Meanwhile, Alice concludes that Gallico must have been disguised as Ormond/Jamison and she and Frank reveal their suspicions to Alan, then to Karen, who is stunned and doubtful. They attend Rinaldi's show and Karen admits it could be Gallico in disguise. Alan asks Karen to stall "Rinaldi" at the theater while he and Alice go to the workshop to get Gallico's prints. When Gallico appears as himself, however, Karen is confused and fails to delay him. She hurries to a local shop to telephone the workshop to notify Alan and Alice, but Gallico arrives in time to answer the phone and hear Karen's blurted warning. Alice hides outside on the fire escape as Alan tries to explain needing the fingerprints. Gallico pretends to submit, then knocks Alan out and places him on the crematorium conveyer belt. Karen has rushed to the workshop and Alice calls down to her, ordering her to distract Gallico in some way. While Gallico warms up the crematorium, Alan revives and Karen pounds on the workshop door, diverting Gallico and allowing Alice to unshackle Alan. The men scuffle as the women call for help, but Gallico ends up unconscious on the now moving conveyer and is killed in the crematorium. Alan receives praise from his superiors for his persistence in the bizarre case. Alan, in turn, credits Alice for her shrewd determination, but she is only interested in her next murder-mystery book.