Mae and Jack are marijuana dealers. They entice local high school kids to stop by Mae's apartment to smoke reefer, laugh fiendishly, dance and play the piano. One day, Jack invites clean-cut Bill and Mary to this den of sin. Bill quickly becomes hooked, and his life plummets. When Mary smokes, she giggles uncontrollably as she is fondled by the bizarre addict Ralph. Bill bursts out of the bedroom to tangle with Ralph, prompting a string of consequences involving deaths, courtrooms and mental institutions, all because of the Devil Weed.