The plot follows a series of murders that occur in a small New England town on Christmas Eve after a man inherits a family estate which was once an insane asylum.

Though attributed to Zora Investments Associates, the film was never registered with the United States Copyright Office and thus fell into the public domain.

Twenty years later, in 1970, lawyer John Carter arrives in East Willard on Christmas Eve with his assistant and mistress Ingrid, having been charged by Jeffrey to sell the house.

After the murders, the killer places a crucifix in Ingrid's hand and proceeds to phone the sheriff, introducing himself as the house's owner and asking him to investigate Carter's disappearance.

Failing to locate the sheriff, Jeffrey returns to the mayor's home, where Diane tells him she has received phone calls for her father from someone named "Marianne" who beckons her to the mansion.

The two stop by the newspaper office, where they meet Charlie who reveals that he cannot speak due to laryngectomy, but manages to explain to them (in written notes) that Tess has also gone to the mansion.

He then ended up faking his death in 1950 and has been living anonymously in a nearby mental hospital ever since before escaping earlier that day after reading from a local newspaper about the Butler mansion being put up for sale.

Jeffrey tells Diane that his grandfather/father is still alive, and that the sheriff, Tess, Towman and the mayor were all former inmates Wilfred sought revenge on for the death of Marianne.

Additionally, Candy Darling, Ondine, Tally Brown, Charlotte Fairchild, Lewis Love, Harvey Cohen, George Trakas, Susan Rothenberg, and Jack Smith appear as various party guests and psychiatric inmates in the film's flashback sequences.

[8] Biographer Tom Weaver notes that the film features commentary on power structures and the "polite society" of small communities.

In the canon of modern gothic themes, the evil asylum occupies roughly the same position held in the nineteenth century by the unholy convent.

[15][1] The production budget was between $212,000[1] and $295,000,[2] The James William Beekman house (also known as The Cliffs estate) in Oyster Bay served as the Butler home in the film.

[16][17] The production was marked by technical issues early on due to inclement weather, resulting in electrical outages and camera operating equipment freezing in the cold temperatures.

"[1] In a retrospective interview, Woronov recalled making the film a "terrible" experience: "We were given a weird script, and Ted [Gershuny] tried to spark it up.

"[9] Post-production took place in the summer of 1972, with director Gershuny and editor Tom Kennedy completing dubbing, scoring, and sound effects with re-recording engineer Raun Kirves.

[33] The film was also shown on Elvira's Movie Macabre, part of WWOR-TV's Fright Night beginning in 1978, and became a staple of late-night television in the November and December months.

[12] In subsequent years, it has been made available on DVD from various entertainment companies that specialize in public domain films, though many of the prints on these editions are of extremely poor quality.

[12] The same print was also used for a DVD release by boutique company Code Red in 2013, in a limited edition double feature paired with Invasion of the Blood Farmers (1972).

[41] In an article by Boston.com ranking the scariest films of all time, it placed at number 59, and was heralded as a "forgotten classic" and "the movie that birthed the modern slasher flick.

"[6] A review published by the magazine Castle of Frankenstein in 1973 was unfavorable, noting that the film appeared to have been "re-edited and reworked to such an extent in the intervening period that it makes little sense in its final form, although the plot had some potentially clever angles...  otherwise, [it is] a hopeless jumble constricted by flashbacks-within-flashbacks, off-on narration by two different characters, [and] clumsy direction.

"[32] Writer Matthew DuPée notes that the film has received substantial criticism for its convoluted plot and "gritty" cinematography, but asserts that it is "propped up by a fascinating location, strong acting and a visceral story.

"[8] DuPée later added, "director Ted Gershuny’s highly stylistic approach, an amazing location, a competent cast, and a dreary and dark script that was ahead of its time.