The film was followed up by seven sequels (most of which are in-name only), beginning with Demons 2 in 1986.
On the Berlin subway, university student Cheryl gets off at her stop in the deserted subway station and is pursued by a mysterious, masked man. Rather than attacking her, the man offers her tickets to a free screening at the Metropol, an isolated and recently renovated local cinema. Cheryl talks her friend Kathy into going with her and they skip class to go see the film. At the crowded theater, they meet two preppy college boys, George and Ken, who take an immediate liking to the girls and help them get a can of cola out of the vending machine. The four sit together in the theater.
There are many people from all walks of life in the audience; a blind man and his guide daughter, an elderly married couple, a boyfriend and girlfriend, and a pimp named Tony along with his two prostitutes who look at the theater's display props in the foyer. One of the prostitutes, Rosemary, scratches her face with a bizarre display mask before they go in to watch the film. The film being shown is a violent, disturbing horror film which features a look-alike of the mask from the lobby; it is about four teenagers who discover an old tomb and dig up the grave of a sixteenth-century fortune teller called Nostradamus. When the teenagers dig up Nostradamus's coffin, they find no body and instead an old book and a mask identical to the strange mask in the foyer. When one of the movie's characters puts the mask on and is scratched by it just like Rosemary was by its doppelganger, he then turns evil and slaughters his friends with a kitchen knife.
Rosemary feels ill and goes to the bathroom, where the scratch on her face bursts open and spews out pus, she then transforms into a bloodthirsty, red-eyed demon like the one in the film. Rosemary attacks her friend, Carmen, who then rips through the screen and transforms into a demon in front of the rest of the cinema-goers. The group of uninfected people race to any exit they can find, only to find that they have all been bricked up making escape impossible. Although they attempt to barricade themselves in the balcony, many are attacked and infected by the demons. One of the demons escapes into the city when four punks break into the building through a back entrance; the punks are soon transformed into demons as well.
In the cinema, only George and Cheryl remain uninfected. Using a display motorcycle and sword props from the foyer, they ride through the auditorium, slicing down many demons. George kills nearly all of them when suddenly, a helicopter crashes through the roof. George and Cheryl use an emergency grappling hook and winch to climb to the roof, where they are attacked by the mysterious man from the subway. They are able to kill him by impaling his head on an exposed bit of rebar. The two climb down to the street and discover that the demonic infection has spread throughout Berlin. They are then chased by a horde of demons before being picked up by a jeep of well-armed survivors (a father and his two children) and they make their escape. As they drive out of the city to safety, Cheryl transforms into a demon and is shot by one of the other passengers, having her body fall out of the jeep and onto the road. With George being the cinema's last survivor, he escapes with the family in the jeep into a distant unknown future.
Dario Argento had an important influence on Dèmoni. In addition to co-writing the script, he also produced the film. Argento's daughter, Fiore, plays the character of Hannah. Michele Soavi, a devotee of Argento's work and his assistant director on several films, also served as an assistant director on Dèmoni and has two starring roles, as the man wearing the silver mask and as Jerry, one of the characters in the film playing at the Metropol. Nicoletta Elmi, who plays the usherette, appeared in Argento's 1975 classic giallo Deep Red, and she also had a small role in the 1971 horror film Twitch of the Death Nerve (directed by Mario Bava, the father of Dèmoni director Lamberto Bava).
Most of the interior cinema scenes were shot in an actual closed down movie theatre. The building still exists but is now a bank. At the same time, the building used for the exterior shots of the movie theatre still exists; it's a club called "Goya", whose appearance in the film has brought it fame and regularly hosts horror conventions today. Filming took place in Germany and Italy, and as a reference to these countries' cinema, posters for Werner Herzog's Nosferatu: Phantom der Nacht and Argento's Four Flies on Grey Velvet can be seen hanging in the Metropol's lobby.
Demons was released theatircally on 4 October 1985 in Italy.
Demons holds a 56% approval rating on review aggregator website Rotten Tomatoes based on nine reviews. Leonard Maltin gave the film 1 1/2 out of 4 stars, criticizing the film's lack of characterizations, logic and plot.
The film was listed at number 53 on US TV channel Bravo's The 100 Scariest Movie Moments countdown.
The soundtrack was released on LP. It has 1980s rock and heavy metal themes, while the sequel was pop and new wave oriented. The soundtrack was performed live for the film's twenty-year anniversary at Shock Pop Comiccon in February 2015. The instrumental soundtrack was composed by Claudio Simonetti.Billy Idol - White Wedding
Accept - Fast as a Shark
Mötley Crüe - Save Our Souls
Claudio Simonetti - Demon
Claudio Simonetti - Killing
Claudio Simonetti - Out of Time
Rick Springfield - Walking on the Edge
Pretty Maids - Night Danger
Go West - We Close Our Eyes
The Adventures - Send My Heart
Saxon - Everybody Up
Some of the films mentioned below are not sequels, and are related in title only as a marketing strategy to gain popularity.