Plot

It's bad enough that boarding school students Samantha and Clara can't go home for the holidays, but things take a deadly turn when a murderous gang arrives on their doorstep - just in time for Christmas.

On 22 December 1971, four sadistic murderers known as The Christmas Killers are terrorizing the town, killing couples at home. At the Blackvale School for Girls, the teenager Samantha Kramer is forced to spend Christmas at the boarding school since her stepfather will travel and will be not available to take her. Now she will spend Christmas with the outcast teenager Clara, who never leaves the school; her teacher Miss Rose Tanner, who will stay with the girls; and the handyman Jimmy, who is Rose's boyfriend and intends to propose her. Meanwhile, The Christmas Killers are driving on the road and the driver, Doug, is drinking and hits a reindeer on the road. A police officer stops his car to help them and is murdered, but hits Doug in the shoulder. Soon, the sadistic killers Maisie, Jude, Doug and Grant arrive at Blackvale School and subdue Rose, Jimmy, Samantha and Clara. They kill Jimmy and explains that Maisie studied at the school and intends to summon the devil to all of them become powerful. They kill Rose and wait for the devil. However, they do not know that the devil has already been unleashed and is waiting for them to be released from the school, and lured Maisie to set him free.—Claudio Carvalho, Rio de Janeiro, Brazil

Clara and Samantha, two students at Blackvale Academy, an all-girls boarding school, have chosen to spend Christmas with their teacher, Rose, and her boyfriend, Jimmy. With a series of ritualistic killings inspired by a demon summoning ritual Maisie learned while attending Blackvale, Jude, Maisie, Grant, and Doug have been terrorizing the neighboring towns. The murderers are forced to seek safety in Blackvale after a fortuitous run-in with a police officer. There, they swiftly apprehend and take Rose and the others into custody, killing Jimmy in the process. They are irritated when the promised demon fails to appear, so they decide to kill Rose in order to complete the ritual at Blackwood.

Together with Jude, Maisie goes to the basement to look through the spell book from which she got the spell. There, she finds that she only got a portion of the ritual and that the ultimate sacrifice must be an unwholesome person. Clara, Samantha, and Grant are left alone when Doug pursues them. Jude behaves oddly and then leaves. As Maisie reads the spell, she understands that Clara, a demon, is supposed to be set free by the ritual. After that, we see Clara using her abilities on Grant to force him to release Samantha, telling her to leave her behind and run for her life. The demon then uses her abilities to take over Grant's mind, using him to seize Jude, Maisie, and Doug and make them unconscious. Samantha calls the police and escapes to a security station, but she decides to go back to save Clara.

When Maisie wakes up, she finds that Clara has left them naked in order to finish the ritual. Clara reveals that centuries ago, when the townspeople summoned her, they changed their minds and she was imprisoned inside the school walls. Clara makes them give up a number of personal things, which leads to Doug and Jude's deaths. After Maisie successfully overthrows Clara's hold on Grant, he commits suicide. When Samantha returns, she learns that Clara is the demon, which further breaks Clara's hold and releases Maisie, who starts to run in just her underwear. Samantha tells Clara, who is upset, that she could not leave a friend behind when she asks why she came back. They quarrel because Clara does not think anyone could be interested in her. She begs Samantha to kill Maisie and release her as she flees into the snow. Samantha obeys, and at the end of the movie, she and Clara depart to explore the world.