The Being

In the town of Pottsville, Idaho, citizens begin disappearing. Young Michael Smith, son of Marge Smith (Dorothy Malone), is the first to vanish. A young man is decapitated while fleeing from an unseen assailant, and three patrons at a drive-in theater are brutally murdered. At each scene, green slime is found. Wanting to get to the bottom of the disappearances but afraid that the publicity might damage the town's potato business, Mayor Gordon Lane (José Ferrer) hires chemical safety engineer Garcon Jones (Martin Landau) to investigate. Also investigating the disappearances is Detective Mortimer Lutz (Bill Osco), who suspects that something terrible has befallen the town.
Meanwhile, more people disappear, and a puddle of green slime is found at each site. With this new string of disappearances, Lutz suspects that Jones knows more than he will admit. His suspicions grow when he's attacked by something monstrous at home, and he barely manages to escape. Lutz confronts Jones about the incident but is told there's nothing wrong in the area.
The following night, while Lutz takes his waitress girlfriend Laurie (Marianne Gordon) home, they're suddenly attacked by a hideous creature. After holing themselves inside a diner, they lock it inside a freezer. The couple then contact Mayor Lane, however, when he arrives, they discover that the creature has vanished, leaving behind a puddle of green slime. In light of this recent attack, Lutz confronts Jones again, who then admits that a highly radioactive creature is responsible. It's revealed that the town is home to one of 2,000 nuclear dump sites in the U.S., and the creature (who's implied to be Michael Smith) is the resulting mutation due to repeated exposure to the site's radioactive materials. The mutant, while intelligent, is completely psychotic but sensitive to light and is inactive during the day.
Arming themselves with shotguns, Jones and Lutz eventually track the creature down to an abandoned warehouse, where the hungry mutant stalks them. Jones is soon attacked and disemboweled by the creature, leaving Lutz alone to fend off the creature. Donning a gas mask, Lutz attempts to kill the creature with poison gas, but it seems unfazed by the poisonous fumes and tosses Lutz around like a ragdoll. As the creature advances, Lutz manages to toss a beaker of acid into the creature's face, momentarily stunning it. Taking advantage of the creature's distraction, Lutz grabs a nearby axe and hacks the creature to death, ending the reign of terror.
A new mutation is seen bursting from the ground.