The story opens with a stern Lecturer addressing an audience of anxious parents, warning them of the insidious dangers of marijuana, which he claims instantly drives youth to depravity, madness, and murder. To illustrate his point, the Lecturer tells the tragic tale of Jimmy Harper and Mary Lane, two wholesome, innocent high school sweethearts living in a idyllic 1930s suburb. Their promising futures are abruptly derailed when charismatic neighborhood bad boy Jack Logan and his brassy, world-weary girlfriend Mae open a local "reefer den" alongside their eccentric, piano-playing associate, Ralph.Seeking a thrill, the naive Jimmy is lured into the den by Jack under the deceptive guise of trying a harmless "tobacco" cigarette. One puff of the devil's weed instantly transforms the sweet-natured Jimmy into a sweating, wide-eyed maniac gripped by violent delusions. Driven by insatiable urges and warped perceptions, Jimmy completely loses his moral compass. His innocent girlfriend Mary, desperately seeking to rescue him from this perceived peril, ventures into the den herself. In a harrowing sequence, Mary is accidentally killed during a chaotic struggle fueled by the drug-induced hysteria of the room's patrons.Jimmy is promptly arrested and put on trial for murder, plagued by terrifying, surreal hallucinations of dancing corpses, a demonic Uncle Sam, and a sultry, seductive Jesus Christ who urges him to indulge further in his wicked impulses. Throughout the trial, the frenzied public clamors for blood, completely brainwashed by the sensationalized rhetoric of the Lecturer and the corrupt local media. The prosecutor argues that marijuana is the ultimate root of all societal evil, pushing otherwise good people past the point of no return.In a shocking and bleak climax, the madness reaches its absolute zenith. Ralph, entirely unhinged by paranoia and psychosis, violently attacks Mae, murdering her
in cold blood before being restrained. Jimmy, overcome by remorse, despair, and the lingering, fractured psychosis of his addiction, is condemned by the court. Rather than facing the
electric chair or a lifetime of institutionalized torture, Jimmy leaps to his death from a high courtroom window, meeting a tragic and untimely end.The film violently snaps back to the present day, where the Lecturer finishes his cautionary tale to the still-terrified parents. Suddenly, the Lecturer, Jack, Mae, Ralph, and the rest of the cast reemerge as smiling, enthusiastic zombies. They joyfully consume the fatal weed themselves, dragging the horrified parents and the entire audience into a fiery, apocalyptic musical finale. The newly corrupted crowd dances wildly into the flames, proving that the reefer madness has successfully consumed the entire world, leaving no one pure, innocent, or safe from its wicked grasp.