The story centers on a young engaged couple whose car breaks down in the rain near a castle where they seek a telephone to call for help. The castle or country home is occupied by strangers in elaborate costumes celebrating an annual convention. They discover the head of the house is Dr. Frank N. Furter, an apparently mad scientist who actually is an alien transvestite who creates a living muscle man in his laboratory. The couple are seduced separately by the mad scientist and eventually released by the servants who take control. The film is based on the 1973 musical stage production The Rocky Horror Show, with music, book, and lyrics by O'Brien. The production is a parody tribute to the science fiction and horror B movies of the 1930s through to the early 1960s.

References:
https://en.wikipedia.org/wiki/The_Rocky_Horror_Picture_Show