A disheveled man in a suit wanders down the main street of the small, rural town of Mountaincrest on a winter's night. He goes into a bar, telling the bartender that he does not know who or where he is. Local thug Joe Mitchell demands his money as he leaves. As the two men struggle in an alleyway, Ma Everett sees only four legs sticking out onto the sidewalk but hears an animal snarling. Two of the legs go limp. Someone- or something- steps out of the alley. She screams, and it runs off into the darkness. Sheriff Jack Haines takes Joe's body to Dr. Jonas Gilchrist and nurse Amy Standish. Gilchrist notes that the wounds seem inflicted by a wild animal, but Ma described not an animal but "a thing." Jack organizes a posse to find the creature. Jack brings Deputy Ben Clovey to Gilchrist's office. Ben has been attacked by "the thing." He describes it haltingly to Jack: "Maybe it had hands covered with hair... or maybe it had paws like a wolf... but it wasn't
all wolf... I didn't have much time to see." Jack declares that a werewolf attacked Ben. Gilchrist and Amy conclude that Jack is correct. The disheveled man arrives at Gilchrist's office. After an automobile accident, he can recall being to two doctors- he does not know who or where they are. He is tormented by what is happening to him. He says he killed Joe, then flees when Amy attempts to give him a sedative, exclaiming, "Those other doctors did something to me!" Amy phones the sheriff. Doctors Morgan Chambers and Emery Forrest discuss the man they had treated after his car crash. They had injected him with "irradiated wolf serum", never before used on humans. The doctors believe that once perfected, the serum will allow "a select minority of people" — chosen by them — to survive the imminent
nuclear holocaust.
Lycanthropy is an unfortunate side effect. The amnesiac man's wife, Helen Marsh, and their preteen son Chris show up and identify the man as Duncan Marsh. The doctors head to Mountaincrest, hoping to avoid blame by killing Duncan. Forrest corners Duncan in a mineshaft. Duncan pleads for his life before suddenly transforming into the werewolf. He attacks Forrest but is driven off by shots fired by Chambers. Amy convinces Jack to try to take Duncan alive and volunteers to help with first aid. Jack reluctantly agrees to allow Helen and Chris to come also and they, accompanied by Ben, set out. Helen calls Duncan with Jack's megaphone. In human form, Duncan comes and tearfully embraces Helen and Chris, but tells Amy to take them away as he fears he might turn into a werewolf again and harm them. Duncan is put in a jail cell. Chambers and Forrest force their way into the jail and try to inject Duncan with something deadly. Duncan changes into the werewolf, kills them and again escapes into the woods. The werewolf, on a bridge, attempts to flee but is shot dead by the posse. As the werewolf dies, it reverts to Duncan's human form. ==Cast==