In medieval Germany, a band Teutonic Knights massacre a village of supposed devil-worshipers and bury their bodies underground, building a Gothic cathedral over the mass grave as a means to contain the demonic evil within.
In the present day, the church's new librarian (Tomas Arana) breaks the seal of the crypt out of curiosity and releases the evil spirits contained beneath it. At the same time, the church's automated mechanisms, which were set up by the architect who built the church, are triggered, causing the doors to close and trapping everyone inside, including a group of visitors.
Father Gus (Hugh Quarshie), the only person not affected by the demons, eventually finds the way to make the church collapse on itself but dies in the process of doing so. Soon after, Lotte (Asia Argento), the sacristan's daughter and the sole survivor of the incident, is seen walking towards the ruins of the church. She finds the seal of the crypt, opens it and peers inside. Blue light emits from within, just like when the librarian first opened it, and she smiles.
The film is loosely based on the short story The Treasure of Abbot Thomas, insofar that it adapts the central premise of a librarian working at a gothic cathedral shrouded in a dark, supernatural past. Writers Dario Argento and Franco Ferrini initially conceived the film as the third and final entry in the popular Dèmoni series; however, director Michele Soavi, a long-time protege of Argento who had served as assistant director on several of his film, insisted that the film stand alone and not connected with the first two entries, rewriting it to remove any direct references to the previous films or their mythology. Soavi has derisively referred to them as "Pizza Schlock", and expressed that he wanted The Church to be more sophisticated. In an interview with Cinefantastique, Soavi explained that he wished to move beyond with his creations following the film's release, and because of that he parted ways with Argento, ending their long-time creative partnership. Though only Soavi, Argento, and Ferrini are given on-screen writing credits, additional rewrites were made by Dardano Sacchetti and Lamberto Bava, with the film's medieval prologue being penned by Bava's brother Fabrizio. English-language dialogue was written by ADR director Nick Alexander, bringing the total number of writers on the film, credited or otherwise, to eight.
Argento and Soavi originally intended for the film's titular church to be St. Lorenz Church in Nuremberg, even performing several test shots there, but city officials objected to the location's use in a horror film. The production ultimately settled on using Matthias Church in Budapest, an archetecturally-similar and historically significant location that is the real-life burial ground of both Béla III and Agnes of Antioch. The film utilized the location for both its late gothic-style exterior and massive interior congregation hall, as well as prominently featuring its iconic pulpit. The remaining majority of interiors were shot on studio sets in Rome, while additional exteriors were filmed in downtown Hamburg, Germany.
The film's visuals contains many allusions and references to religious artwork. The design for the reptilian gargoyle demon is taken directly from an infamous 17th century woodcut of a man selling his soul, while the image of a naked woman embracing the demon is a lifted from the painting "Vampire's Kiss" by fantasy artist Boris Vallejo.
As with many Italian genre films of the period, the film was released under a myriad of alternative titles, including Demons 3, Demons 3: The Church, Demon Cathedral, Cathedral of Demons, and In the Land of Demons.
The film's score was composed by prog-rock musician Keith Emerson, composer Philip Glass, and the band Goblin, whom had previously collaborated with writer/producer Argento on several prior films, including Suspiria and Tenebrae. In additions to original compositions, the soundtrack features excerpts from Glass' 1981 chamber music piece Glassworks and additional tracks by Simon Boswell and Fabio Pignatelli.
The film premiered in Rome on 10 March 1989 and was released in the Italian cinemas on the same day. It received similar wide releases in both Japan and Spain, and a limited release in the United States before being released on videocassete.
In a contemporary review, Variety referred to the film as a "technically proficient but empty horror exercise". The review noted that the musical score by Goblin was The Church's "strongest element."
On review aggregator website Rotten Tomatoes, The Church currently has an approval rating of 64% based on eleven reviews, satisfying the "Fresh" criteria. Allmovie called it a "gothic-drenched apocalyptic nightmare" that builds "a suffocating sense of quiet dread".