The film is set in the village of Nomen Tuum (Latin, "your name"), which has a well that can heal the sick and make a person more beautiful.

A prominent young succubus named Kia (Allyson Ames) loathes the routine of herding sinners to hell.

She soon stumbles upon a suitable victim: Marc (Shatner), a young soldier, who with his sister Arndis (Ann Atmar) comes to the sacred water in order to heal his battle wounds.

† Uncredited After the ABC Television Network cancelled producer Leslie Stevens' science fiction series The Outer Limits in 1965, Stevens wrote a horror script to make use of the talents of the Outer Limits team he had brought together – including cinematographer Conrad L. Hall and composer Dominic Frontiere – with an eye to marketing it to art houses.

The script was translated into Esperanto, and the actors rehearsed for 10 days to learn their lines phonetically, but no one was present on the set to correct their pronunciation during shooting.

Location shooting took place at Big Sur Beach and at the Mission San Antonio de Padua near Fort Hunter Liggett in Monterey County.

[1] The premiere of Incubus took place at the San Francisco Film Festival on October 26, 1966,[4] where, according to producer Taylor, a group of 50 to 100 Esperanto enthusiasts "screamed and laughed" at the actors' poor pronunciation of the language.

When producer Anthony Taylor attempted to prepare Incubus for home video release in 1993, he was told by the company that stored the negative, film elements, and prints, that all were missing and presumed to have been destroyed in a fire.

[6] On February 14, 2023, CineSavant stated that Le Chat Qui Fume reported that a new 35mm print with "excellent" image quality has been located.

[8] Stanley Eichelbaum of the San Francisco Examiner called the film "a dud, so pretentious and arty that it nearly drowns in dull, studied technique.

[10] TV Guide rated the film one out of four stars, calling it "Inept, pretentious, and dull once the novelty wears off, but handsomely shot in Big Sur".