In the town of Canyon Valley, when the members of the Metaphysical Bowling Society are murdered during their annual picnic, Detective Sergeant Wino, the head of the police department, vows to find their killer. That night, Joe Putzman, the town’s unctuous T.V. newscaster, reports on the “banana murders,” named for the banana peels found at the scene of the crime. Because the bodies were torn apart, the pieces have been stuffed into plastic bags and no one has been able to determine the number dead. Putzman announces that his station is offering a prize to the first viewer to estimate correctly the number of bodies the bags contain. Meanwhile, in a field nearby, teenagers Barbara, Betty, Bobby and Billy find a skull and some banana peels. Billy brashly calls to the killer, and when he goes to investigate, falls into a hole leading to a subterranean cave. Betty, Bobby and Barbara join him in the cave, where they find a trail of blood. After Billy disappears into the dark recesses of the cave to follow the trail, the others hear his screams, and despite the girls’ objections, Bobby goes to Billy's aid and disappears into the dark. The girls escape, however, and report the cave to Detective Wino. Wino calls Professor Shirley Shlibovitz to meet him at the site of the cave, and when Shlibovitz arrives there, Putzman interviews him about the banana killer. Shlibovitz theorizes that the killer is a “Schlockthropus", the missing link between ape and man, who had been frozen at the onset of the ice age 2,000,000 years ago. While Shlibovitz climbs into the cave to investigate, Putzman introduces the winner of his station’s Body Count Contest, Lenore Binerman, the sponsor of the upcoming high school dance. After accepting the award, Lenore relates that her blind daughter Mindy has just had surgery, which may enable her to see for the first time in three years. Schlock then suddenly appears, and when Putzman tries to interview him and holds out his hand to shake, the beast rips off his arm. The bystanders flee, and when Detective Wino tries to handcuff Schlock, the beast becomes angry, sending Wino running away in fear. Soon after, Mindy comes home from the hospital, her eyes still bandaged, and as she rests in the backyard, Schlock climbs over the fence and falls in love with her at first sight. Feeling his furry coat, Mindy thinks that he is a dog and fondly pets him. After Mindy’s bandages are removed, she sees her boyfriend Cal for the first time, then goes into the yard to find the stray dog. When Schlock sees Cal kiss Mindy, he becomes jealous and rips down the fence, sending the terrified Mindy scurrying into the house. Cal protects Mindy and yells at Lenore to retrieve some flares from his car. Using the flares to frighten Schlock, Cal escapes with Mindy and Lenore, leaving the beast trapped in the house. Wino arrives soon after, but Schlock breaks down the door and rampages onto the street, knocking down Wino in the process. The night of the big dance, four police officers are posted around the gym where the dance is to be held. However, Schlock easily overpowers the officers and stalks into the gym, causing the students to flee in panic. When Schlock lumbers toward Mindy, she passes out in fright and he sweeps her up into his arms and walks off. Wino calls the National Guard for reinforcements, and by the time they arrive, Schlock has climbed onto the gymnasium roof, still cradling Mindy in his arms. Requisitioning some flares from the Guardsmen, Cal begins to pelt Schlock, who drops Mindy. After Cal grabs Mindy and runs to safety with her, the beast leaps onto the ground, and the Guardsman hit him with a volley of gunfire. Dropping to his knees, Schlock reaches out to Mindy, gazing at her with a mournful look of yearning. After Schlock collapses and dies, Wino observes that it was beauty that killed the beast. Some time later, Shlibovitz emerges from the cave, holding baby Schlock in his arms.