Don Gallico Vincent Price is a master of disguise and inventor of stage-magic effects, an aspiring star magician who dreams of headlines under the banner Gallico the Great in the late 19th century. Posing as his rival, The Great Rinaldi John Emery, he launches a bold first show featuring his latest illusion, The Lady and the Buzz Saw. The performance is halted when Ross Ormond [Donald Randolph], a sharp businessman, and his lawyer arrive with a cease-and-desist order. Ormond heads Illusions, Inc., a trick provider that claims ownership over all of Gallico’s creations, not just the specific trick for the night, and the clash over control sets the tone for what follows.
Backstage at Illusions, Inc., tension erupts as Ormond and Gallico spar over access to Gallico’s buzz-saw act and the contract that ties all of Gallico’s work to Ormond’s company. Gallico also accuses Ormond of corrupting his wife, Claire [Eva Gabor], who is now married to Ormond, while Ormond retorts that Claire was always a gold digger. In a fit of rage, Gallico decapitates Ormond with the buzz-saw, and places the severed head in a bag. The bag is accidentally taken by Karen Lee [Mary Murphy], Gallico’s assistant, when she stops by to meet her boyfriend, Lt. Alan Bruce [Patrick O’Neal], the police detective. The bag is later left in a hansom cab, and the cabbie turns it over to the police; Gallico lets the police believe the bag contains a dummy head, preserving his ruse for the moment.
Gallico continues his deception by impersonating Ormond to rent an apartment from Alice Prentiss [Lenita Lane], an author of mystery novels. Prentiss notices oddities, and Gallico, in Ormond’s body, uses a dummy to appear in a bonfire celebration. Ormond’s skeletal remains are found among the ashes, intensifying the mystery. Claire, unsettled by the loss of her husband and the strange apartment, confronts Gallico and recognizes him in disguise, deducing that he murdered Ormond. When Claire screams, Gallico strangles her to prevent exposure and escapes before Prentiss arrives in response to the commotion.
The case grows more tangled as the fingerprints on Claire’s throat—left while Gallico impersonated Ormond—influence the police to conclude that Ormond was the killer. Master of Ceremonies [Roland Varno] tracks the inconsistencies and hints that the prints may not belong to Ormond at all, casting doubt on the case. To seal the illusion, Gallico unveils a new act, The Crematorium, and appears to be incinerated in a furnace built for the show. In a confrontation, The Great Rinaldi [John Emery] reveals his deduction that Gallico murdered Claire while wearing a mask and impersonating Ormond, and he attempts to blackmail Gallico into handing over all future illusions. Gallico murders Rinaldi and incinerates his remains in the furnace, then impersonates Rinaldi to take over the tour, keeping the police from tracing him by shrouding the murder in theater roles.
Prentiss begins to sense the strange connection between Gallico and Ormond, and she alerts Lt. Bruce that Gallico may be the mastermind behind the impersonations. Bruce and Prentiss decide to obtain Gallico’s fingerprints, hoping to untangle the web of identities. Gallico, in the guise of Rinaldi, resists and tries to obstruct their investigation. Meanwhile, Prentiss pieces together the pattern of impersonations and the link between the missing Ormond and the false identities that have surrounded him.
The climactic pursuit unfolds as Bruce and Prentiss break into Gallico’s workspace to retrieve solid evidence. Gallico returns just in time, knocks Bruce out, and prepares to burn him in the furnace. Prentiss signals for help, and Karen Lee pounds on the door outside, creating a distraction. Prentiss frees Bruce from his bonds just as the struggle reaches a fever pitch. In the final confrontation, Bruce manages to knock Gallico into the furnace, where he is incinerated, bringing the murderous illusion to a literal blaze and offering a grim, ironic end to the man who treated stage magic as a deadly weapon.
