Horror High [1973]

Vernon Potts, a reserved and amiable prodigy attending high school, embarks on a daring scientific endeavor by conducting experiments with a chemical substance. This chemical, when administered to his beloved guinea pig named "Mr. Mumps," unexpectedly transforms the once docile creature into a ferocious and insatiable monster. Tragically, Vernon's world takes a dark turn when the eerie janitor, Mr. Griggs, cruelly forces him into ingesting the same chemical after ruthlessly killing Mr. Mumps. Overwhelmed by a surge of anger, Vernon retaliates by ending Mr. Griggs' life and concealing the lifeless body. Driven by an all-consuming desire for vengeance, Vernon embarks on a relentless killing spree, targeting those who relentlessly tormented and belittled him. Among his victims are Coach McCall, the stern gym instructor, Roger Davis, the school's popular jock, and Ms. Grindstaff, his spiteful English teacher. Despite his success in exacting retribution, the chemical concoction has unleashed a Jekyll and Hyde transformation within Vernon, causing him to oscillate between his former self and a malevolent alter ego. Consequently, he becomes the subject of a relentless pursuit led by the determined Lieutenant Bozeman, who diligently investigates the series of murders.