A criminologist narrates the tale of the newly engaged and innocent couple, Brad Majors and Janet Weiss, who find themselves lost and with a flat tire on a cold and rainy late November evening, near a town called Denton in 1974. Seeking a telephone, the couple walks to a nearby castle where they discover a group of strange and outlandish people who are holding an Annual Transylvanian Convention. They are soon swept into the world of Dr. Frank-N-Furter, a self-proclaimed "sweet transvestite from Transsexual, Transylvania". The ensemble of convention attendees also includes servants Riff Raff, his sister Magenta, and a groupie named Columbia.
In his lab, Frank claims to have discovered the "secret to life itself". His creation, Rocky, is brought to life. The ensuing celebration is soon interrupted by Eddie (an ex-delivery boy, both Frank's ex-lover and Columbia's current partner, as well as partial brain donor to Rocky) who rides out of a deep freeze on a motorcycle. Eddie then proceeds to seduce Columbia, get the Transylvanians dancing and singing and intrigue Brad and Janet. When Rocky starts dancing and enjoying the performance, a jealous Frank kills Eddie with a pickaxe. Columbia screams in horror, devastated by Eddie's death. Frank justifies killing Eddie as a "mercy killing" to Rocky and they depart to the bridal suite.
Brad and Janet are shown to separate bedrooms, where each is visited and seduced by Frank, who poses as Brad (when visiting Janet) and then as Janet (when visiting Brad). Janet, upset and emotional, wanders off to look for Brad, when she discovers Frank in bed with Brad (who is smoking a cigarette) on a video monitor. She then discovers Rocky, cowering in his birth tank, hiding from Riff Raff, who has been tormenting him. While tending to his wounds, Janet becomes intimate with Rocky, as Magenta and Columbia watch from their bedroom monitor.
After discovering that his creation is missing, Frank returns to the lab with Brad and Riff Raff, where Frank learns that an intruder has entered the building. Brad and Janet's old high school science teacher, Dr. Everett V. Scott, has come looking for his nephew, Eddie. Frank suspects that Dr. Scott investigates UFOs for the government. Upon learning of Brad and Janet's connection to Dr. Scott, Frank suspects them of working for him; Brad denies any knowledge of it, and Dr. Scott assures Frank that Brad is not involved in UFOs. Frank, Dr. Scott, Brad, and Riff Raff then discover Janet and Rocky together under the sheets in Rocky's birth tank, upsetting Frank and Brad. Magenta interrupts the reunion by sounding a massive gong and stating that dinner is prepared.
Rocky and the guests share an uncomfortable dinner, which they soon realise has been prepared from Eddie's mutilated remains. Janet runs screaming into Rocky's arms, provoking Frank to chase her through the halls. Janet, Brad, Dr. Scott, Rocky, and Columbia all meet in Frank's lab, where Frank captures them with the Medusa Transducer, transforming them into nude statues. After dressing them in cabaret costumes, Frank "unfreezes" them, and they perform a live cabaret floor show, complete with an RKO tower and a swimming pool, with Frank as the leader.
Riff Raff and Magenta interrupt the performance, revealing themselves and Frank to be aliens from the planet Transsexual in the galaxy of Transylvania. They stage a mutiny and announce a plan to return to their home planet. In the process, they kill Columbia and Frank, who has "failed his mission". An enraged Rocky gathers Frank in his arms, climbs to the top of the tower, and plunges to his death in the pool below. Riff Raff and Magenta release Brad, Janet, and Dr. Scott, then depart by lifting off in the castle itself. The survivors are then left crawling in the dirt, and the narrator concludes that the human race is equivalent to insects crawling on the planet's surface, "lost in time, and lost in space... and meaning".
Tim Curry as Dr. Frank-N-Furter, an eccentric bisexual transvestite scientist
Susan Sarandon as Janet Weiss, a heroine
Barry Bostwick as Brad Majors, a hero
Richard O'Brien as Riff Raff, a hunch-backed handyman
Patricia Quinn as Magenta, a domestic
Nell Campbell (credited as Little Nell) as Columbia, a groupie
Jonathan Adams as Dr. Everett V. Scott, a rival scientist
Peter Hinwood as Rocky Horror, a creation (Trevor White as singing voice)
Meat Loaf as Eddie, an ex-delivery boy
Charles Gray as the Criminologist, an expert
Jeremy Newson as Ralph Hapschatt
Hilary Farr (credited as Hilary Labow) as Betty Munroe
based on the 1973 musical stage production The Rocky Horror Show. The production is a parody tribute to the science fiction and horror B movies of the 1930s through to the early 1960s.