After Professor Frankenstein, a visiting lecturer from England, is severely criticized by his medical college colleagues for his theories regarding body organ transplants, he states that one day he will be proven correct. Upon returning to the laboratory in his house, Frankenstein persuades physicist Dr. Karlton to assist him in assembling a living human being from parts and organs obtained from young cadavers. Frankenstein admits that his ancestor created a monster, but that he intends to produce a perfectly normal human being. While the scientists talk, two cars crash outside the house and the ensuing fire kills the vehicles' teenage occupants. Frankenstein and Karlton recover the body of a teenage youth, his head crushed and face burned beyond recognition, and take it to their laboratory. During his lecture tours in other cities, Frankenstein has assembled a collection of body parts and tells Karlton that now they will now be able to begin the experiment. At a party, Frankenstein asks Margaret, who has been his nursing assistant, to help with a new project. To convince Margaret to move into the house and thus prevent any interruptions to his work, Frankenstein offers to marry her. The next day, Frankenstein and Karlton begin to dismantle the boy’s body, disposing of useless limbs by passing them, via a chute, to an alligator located beneath the laboratory. Later, after several members of a high school track team are killed in an air crash and their partial remains are buried in a local cemetery, the scientists dig up the boys' strong limbs for their experimental subject. With the new limbs attached, Karlton reactivates the body with high-voltage electricity. Although the boy’s head is swathed in bandages and he has only one eye, Frankenstein succeeds in getting his creation to communicate with him. Meanwhile, Margaret, who is unaware of the nature of the experiment, becomes upset by her fiancé's obsession with work and, feeling neglected, tells Frankenstein that she wants to plan their wedding. Angered, Frankenstein slaps her, then apologizes, explaining that his work will soon be finished and they will marry. Later that day, after the scientists leave the house, Margaret makes an impression of the lock on the laboratory door and has a key made. When she unlocks the door, she is horrified by the monster and runs out. Days pass as the megalomaniacal Frankenstein coaches the boy in speech and in total obedience, while Karlton gives him electrical treatments and special vitamins. When the youth becomes restless and wants to go outside to be with people, Frankenstein removes the bandages and shows him his hideously disfigured face in a mirror, but promises to give him a new face eventually. After Frankenstein leaves the laboratory, the boy manages to escape and wanders the streets until he sees, through an apartment building window, a provocative young woman combing her hair. When she spots him, she screams and the monster breaks in, smothers her to death, then runs back to the laboratory. The next day, when Frankenstein reads a newspaper account of the killing, he confronts the boy, who admits his guilt and, fearing that Frankenstein will destroy him, promises to obey him. After Frankenstein becomes enraged when Margaret invites a jeweler to the house to show them engagement and wedding rings, she tells him she knows about the monster. Although the professor appears to assuage Margaret, he later informs the boy that, while he is ready to give him a new face, a certain woman is endangering his plan by threatening to go to the police, and therefore must be stopped. When the professor asks Margaret to help give the boy an injection, he suddenly leaves her alone, and the boy kills her and tosses her body to the alligator. At night, Frankenstein and the boy drive to a parking spot where the boy selects the face he would like to have from among the necking teenage couples. After Frankenstein grafts the chosen face onto the monster, Karlton returns from a trip and Frankenstein proudly shows him his work. Karlton becomes concerned about how the professor accomplished the transformation and about Margaret’s absence. Frankenstein, worried that the monster might be recognized locally, explains to Karlton that he intends to take the boy to England where he will present his creation to fellow scientists. After Karlton points out that the boy will need to have a passport and immigration papers, Frankenstein calmly tells him that he intends to disassemble the boy, preserve the parts and ship them in crates to his laboratory in London. Although Karlton finally realizes that Frankenstein is completely mad and refuses to cooperate further, the professor attempts to strap the struggling boy to the operating table. After Karlton runs out, the boy overpowers Frankenstein, strangles him and feeds him to the alligator. When Karlton returns, accompanied by two patrol officers with guns drawn, the boy falls against an electrical panel and is killed while resisting arrest.