The story is about a succubus who falls in love with a deeply religious soldier (Shatner) she intended to seduce. Outraged by this, her sister summons their leader, a devilish incubus (Milos Milos), who rapes the soldier's sister and attempts to kill him.
The film was performed entirely in the constructed languageEsperanto. This was done to create an eerie, other-worldly feeling, and the director has prohibited dubbing into other languages. The 2001 DVD includes subtitles in English and French, and the restoration was funded by the Sci-Fi Channel. Most English speakers have given the film good ratings and reviews, likening it to the work of Ingmar Bergman, while Esperanto speakers are generally disappointed by the actors' dreadful pronunciation.
It is often stated that Incubus was the first Esperanto film, however this is simply a common misconception: the Esperanto film Angoroj appeared in 1964, one year before Incubus.
Many members of the cast met rather gruesome fates after the film wrapped. Actor Milos killed his girlfriend and himself in 1966. Actress Ann Atmar, who plays Shatner's sister, committed suicide mere weeks after the film wrapped. The daughter of actress Eloise Hardt was kidnapped and murdered. William Shatner starred in a Gene Roddenberry series. These grim events have given rise to a popular rumor that Incubus was a cursed production.