We open with the title and credits written on a makeup mirror using a lipstick. We zoom in on a drawing of the Teenage Werewolf, then dissolve to an actor in Werewolf makeup getting a last minute touchup. The Teenage Werewolf is Larry Drake (Gary Clarke) and the makeup artist is Pete Dumond (Robert B. Harris). Also present is Rivero (Paul Brinegar), Dumond's long-time assistant. Rivero praises his boss as having twenty-five years of experience creating movie monsters for the studio. Dumond walks Larry walk over to the set. They encounter other studio employees and a tour group. On the set, the director, Martin Brace (Thomas Browne Henry) approves, telling Dumond, "Great Pete, just great, exactly what I want." The Teenage Frankenstein character, Tony Mantell (Gary Conway) is brought on set. The director works with each actor rehearsing the final scene of their picture.
In the makeup office, Dumond and Rivero are cleaning up. Dumond likes working with teenagers, "They've got spirit and they cooperate." Two men walk in the office, unannounced and without knocking. They scope out the space, then inform Dumond that they are part of the group that has taken over the studio. They introduce themselves as John Nixon (Eddie Marr) and Jeffrey Clayton (Paul Maxwell). They blithely announce that after the picture Dumond is working on is completed his services will no longer be required. The monster cycle is done and the studio is going in a different direction. Dumond tries to convince the pair that his services are still required, but they are adamant. This starts Dumond over the edge and he vows ominously, "And before I leave this lot I intend to prove I'm right."
That evening Dumond returns to his office. He stops to admire posters of the Teenage Werewolf and Frankenstein and waxes philosophical about his contribution to the financial success of the studio. He vows, "I'll destroy this studio...see it goes up in flames before I." He stops short and reconsiders, then vows to destroy the new owners first using his monsters. Rivero shows up and they enter the makeup room. Dumond explains his plan to Rivero. He will add a drug to the makeup foundation that will render the actors susceptible to hypnotic suggestion. He will direct Tony (Frankenstein) and Larry (Werewolf) to kill the new studio bosses. Two studio guards, Richards (Malcolm Atterbury) and Monahan (Dennis Cross) meet at the guard shack. Monahan complains that nothing ever happens on the night shift.
The next day, Larry stops by the makeup department to have his Teenage Werewolf makeup applied. Dumond tells Larry the makeup department will be closed at the end of the picture he is working on and Larry won't be able to get any future roles. He applies the new makeup formula and starts the hypnosis and tells him the plan. In the Screening Room, Nixon, Clayton, and Banks (an uncredited Herman Cohen) review the rushes for Banks' latest musical. Banks leaves, then Clayton also exits the Screening Room leaving Nixon alone to watch the rushes from the Frankenstein and Werewolf film. From behind, Larry, in full werewolf makeup, attacks and kills Nixon, choking him while growling and foaming at the mouth. Back in the makeup chair, Dumond asks Larry, "Now you're sure my boy? Nobody saw you?" Larry nods in the affirmative. Dumond notices the blood on the Werewolf gloves and directs Rivero to wash the blood out of them. He wakes Larry from his trance.
At the Screening Room, the projectionist is fingerprinted and questioned by the police about the death of Nixon. The doctor examines Nixon's body. He concludes that the time of death was probably 8:34 based on the broken watch and a broken neck is the cause of death. Clayton meets with detectives Thompson (Walter Reed) and Jones (John Phillips). Clayton tells the police that Nixon had no enemies on the West Coast, but they did have to pink slip about one hundred employees at the studio.
Larry Drake and his girlfriend Arlene Dow (Heather Ames) are at a party. Larry complains of not feeling well. He complains of feeling like he blacks out. They rejoin the party. Monahan stops by the makeup department on his security rounds. He asks Dumond, who is working late, why he continues to keep late hours even after being fired. Monahan has been playing detective and tells Dumond that he thinks Nixon's death was an inside job. He infers that Dumond and Rivero may be involved, as they were still on the lot when Nixon was killed. He adds that all his observations including the time they left the lot are noted in his little black notebook, which he waives about provocatively. Monahan continues his rounds on the studio lot. Richards stays in the guard shack listening to the radio. Monahan enters the commissary and is accosted by a visage with a scar running from forehead to chin. He is beaten to death with a hammer or club. His black notebook is taken by the assailant. Back in the makeup department Dumond is cleaning up his face. Richards notes the time Dumond and Rivero leave the lot. Richards gets anxious that his partner, Monahan, has not checked in. He goes to look for him. He finds the body in the cafeteria. Richards calls the police and waits for Jones and Thompson to arrive and start their investigation. Again, Pete Dumond and Riveros names come up as being on scene when the murder occurs. The next morning Jones meets with Dumond to question him. On a sound stage a John Ashley musical number is filmed. When the number wraps, Clayton reminds Dumond, both of whom were on the set, that singing, dancing, and beautiful women are what the public wants and what the studio will produce.
Dumond and Rivero are preparing Tony's Frankenstein make up when they are interrupted by two high school girls from their school newspaper doing an article on the studio. They interview Tony while he is sitting in the makeup chair. After they leave, Dumond applies the drugged foundation then hypnotizes him. Clayton checks out of the studio with Richards on guard that evening. He drives home in his Lincoln convertible and parks in the garage. As he exits his vehicle he is surprised by the Teenage Frankenstein waiting for him. Tony kills Clayton on the front seat of his car, sounding the horn several times. While struggling with his attacker, he gets some makeup on his hands. Tony flees the scene. While running back to Rivera's house, he knocks down a maid, Millie (Pauline Myers) walking down the sidewalk. She screams when she sees his makeup. At the house the two makeup artists remove Tony's mask and take him out of his trance. Rivero is starting to get cold feet as the body count climbs. The pair have been invited to police headquarters for questioning. Dumond reminds Rivero to keep his mouth shut. He'll do all the talking. As they are leaving, Gary Droz (Robert Shayne) arrives. He is Larry Drake's agent and is unhappy with Dumond. He warns Dumond, "You leave my boy alone. Don't you tell him that after this picture is finished that he'll never get another job." He finishes reading Dumond the riot act, then storms off.
While Dumond and Rivero wait to be questioned, Richards tells Dumond he isn't getting any sleep. He spends his nights at the studio and his days being questioned by the police. Police Capt. Hancock (Morris Ankrum), along with detectives Thompson and Jones, questions Mille about what she saw when Clayton was killed. Richards is next to be interviewed. They review the Monahan killing. Finally, Dumond and Rivero are called in for questioning. The police tell the pair that the reason for their questioning is that they suspect the killer or killers may have been in full makeup and they may have information important to solving the murders. Thompson senses weakness in Rivero and starts to browbeat the now rattled assistant. Questioning finished, they are released, and walk to Dumond's car in the parking lot. Dumond is convinced that his sniveling assistant is about crack. Rivero reminds Dumond that Tony and Larry are still to be questioned and they may reveal something. Dumond reminds Rivero that, "Those boys are still under my control." A lab technician (Rod Dana) tells Capt. Hancock and detectives Thompson and Jones that he found greasepaint and putty under the fingernails of Clayton. The pigment and base suggest a homemade blend rather than a commercial product. Hancock orders the tech to accompany him to the studio with his equipment for a spot analysis.
When Dumond and Rivero arrive at the makeup department, Larry and Tony are there waiting. Their supplies have already been packed. Dumond invites the boys to his house and asks them to help move some boxes to his car. Dumond packs a few missed items, but discards a jar of makeup in the trash can. Martin Brace stops by to say goodbye to Dumond. As Dumond, Rivero, Tony, and Larry exit the lot in Dumond's car, the police drive up. They go to the makeup room and discover the discarded makeup in the trash can. The tech analyzes it on the spot.
At Dumond's house, the boys carry the boxes inside. Dumond locks the door and lights some candles. [Note: in this copy of the movie, the cinematography changes from black and white to color for the balance of the film.] The room is decorated with multi-colored curtains and masks of creatures are displayed. Dumond tells the boys the masks are his family and children. Tony and Larry are uneasy and for good reason. Dumond continues to light candles and mumble to himself. He invites the boys to examine the masks while he and Rivero go to get refreshments. The boys begin to exchange information about their encounters with Dumond. Rivero voices his concern about Larry and Tony, "I don't think they can be trusted." Dumond reassures Rivero, but becomes suspicious when Rivero reveals that he intends to leave the state and visit his brother in Arizona. Dumond is now convinced Rivero plans to leave him out to dry with the police. Dumond kills Rivero with a dagger, then moves his body into a closet. Dumond joins the boys in the mask room with refreshments. He hands them glasses of wine. The boys voice their discomfort with Dumond, his ideas, and his desire to, "Add them to his collection." They notice the door to the room is locked and demand to be allowed to leave. Dumond tells Tony and Larry that they were responsible for two of the murders. He pulls a machete on the boys. In their escape attempt they knock over a candle and start a fire in the room. The masks are destroyed as Dumond screams, "My children! I must save my children!" As the room burns, the masks melt and Dumond is consumed by the fire. The police break a window to the home and unlock the door and enter. They force the door and rescue Tony and Larry. We close with a shot of the room fully engulfed in fire.