A troubled teenager seeks help through hypnotherapy, but his evil doctor uses him for regression experiments that transform him into a rampaging werewolf.

After Detective Donovan is summoned to Rockdale High School to break up a fight between students Tony and Jimmy, he advises Tony, who admits to starting the fight and has previously been in trouble, to talk with Dr. Alfred Brandon, a psychologist at the local aircraft plant. Tony declines, but his girl friend Arlene and her parents, as well as his widowed father, continue to show concern about his violent behavior. Finally, after Tony attacks a friend at a Halloween party, he realizes that he needs help and goes to see Brandon. Brandon has his own agenda, however, and feels that Tony will be an excellent subject for his experiments with a serum he has developed that causes the regression of personalities to their primitive instincts. Although Brandon's assistant, Dr. Hugo Wagner, protests that the serum might kill Tony, Brandon begins his treatment and within two sessions suggests to Tony that he was once a werewolf. That night, after Tony drives Arlene home from the teenagers' club, Frank, one of their friends, is attacked and killed as he is returning home. While Donovan and police chief Baker review photographs of the victim and await an autopsy, Pepi, the police station's janitor, persuades officer Chris Stanley to let him see the photographs. Pepi, a native of Europe's Carpathian Mountains, where werewolves, human beings possessed by wolves are common, immediately recognizes the marks on Frank's body. Chris refuses to believe that Frank could have been the victim of a werewolf, however. The next day, after another session with Brandon, during which Tony tells the doctor that he feels that there is something very wrong with him, Tony reports to Miss Ferguson, the high school principal. After Miss Ferguson tells Tony that Brandon has reported a positive improvement in his behavior, she states that she intends to recommend him for entry into the state college. As Tony leaves the principal's office, he passes the gymnasium where a lone female student, Theresa, is exercising. A bell triggers his transformation into a werewolf and he attacks and kills Theresa. Tony runs away and despite the changes in his facial appearance, several witnesses identify him by his clothing, causing Baker to issue an all-points bulletin for his arrest. Doyle, a local reporter, interviews Tony's father as well as Arlene and her parents, in the hope of locating Tony and scooping the story. Baker and Donovan make plans to trap Tony in the woods where they suspect he is hiding and supply their officers with flaming torches, traditionally used against werewolves. Tony, still in the form of a werewolf, watches as the police look for him, but is surprised by a dog, which he kills. By morning, when Tony wakens in the bushes, he has reverted to his normal appearance and walks into the town. After attempting to phone Arlene, he heads to Brandon's office and begs for his help. As Brandon is eager to witness and film Tony's transformation in order to advance himself in the scientific community, he once again injects Tony with the serum. After the transformation, a ringing telephone triggers Tony's instincts and he kills both Brandon and Wagner while the film camera breaks open, ruining the evidence. Alerted that Tony has been seen nearby, Donovan and Chris break in and are forced to shoot several times as Tony advances toward them. Upon dying, Tony regains his normal features, leaving Donovan to speculate on Brandon's involvement and on the danger of man interfering in the ways of God.