The Pyx, also known as The Hooker Cult Murders and La Lunule (French: The Moon), is a 1973 Canadian horror film directed by Harvey Hart and starring Karen Black, Christopher Plummer, Donald Pilon, and Jean-Louis Roux. Based on John Buell's 1959 novel of the same name, it follows a Montreal police detective unraveling the mystery behind the death of a heroin-addicted prostitute who died under bizarre circumstances after falling from a building. Its title refers to the pyx, a small container used by the Roman Catholic Church to hold sacramental bread.Development of a film adaptation of Buell's novel dates back to 1964, when director Curtis Harrington expressed interest in directing a feature film for either United Artists or Columbia Pictures, and in which he considered casting several actors, including James Mason, Ursula Andress, Catherine Deneuve, and Orson Welles. The film was ultimately shot in 1972 by Hart, with Black and Plummer appearing in the principal roles. In addition to acting in the film, Black wrote and performed several original songs featured in it. It was the most expensive film ever produced in Canada at the time, with a budget of approximately $1 million.The Pyx premiered in Canada on September 17, 1973, and opened in the United States the following week through Cinerama Releasing Corporation. It received mixed reviews from critics, with some praising the performances, narrative style, and themes, while others criticized its pacing and screenplay. It also drew a number of comparisons to Klute (1972), another film depicting a murder mystery that involves a prostitute.

The Academy of Motion Picture Arts and Sciences holds the original 35 mm film and optical sound elements of The Pyx in their archive.