In a remote wooded area of New Hampshire, a group of teenagers-two boys and two girls-locate an alter that they believe is used for Black Magic. One of the kids, Dave Duran, jokingly recites an incantation believing it will scare his girlfriend. The joke backfires and the words summon a powerful, evil force. The kids panic and run away from the alter. One of the teenagers, Jerry Stevens, is attacked by the force. A hunter discovers his desecrated body the following morning.

Believing the murder to be the work of a witch cult, Sheriff John Oakes asks the F.B.I. for help. Mulder and Scully examine the corpse from which the eyes and heart have been removed. Mulder's sense that the area has a strange feel is confirmed when toads begin dropping from the sky. Scully attributes the strange event to tornados in Northern Massachusetts. After researching a local library, the agents discover that Duran checked out a book on witchcraft. When questioned, a horrified Duran admits he never thought his words would summon the Devil.

A visit to Crowley High School uncovers signs that the student population suffers from repressed memory. Scully, however, attributes the town's fear to mass hysteria. Mulder notes how water in the city drains in a counter clockwise fashion-against the laws of gravity. He believes a powerful force is at work.

During a science class, a fifteen-year-old girl named Shannon Ausbury suddenly begins screaming when asked to dissect a pig embryo. The agents question the girl. Shannon recounts how her stepfather sexually molested her, a nearly forgotten memory. But she also recounts how her parents friends impregnated her three times and then killed the children. She also claims that Jim murdered her sister during a sacrifice. Mulder and Scully are stunned by the claims and decide to interview her parents.

The Ausburys claim one daughter died of crib death and assure the agents their daughter has never been pregnant. With the town's secret in danger of being exposed, a devil worshiper named Mrs. Paddock, a new teacher at the high school, places a spell on Shannon. Shortly thereafter, Shannon slashes her wrists.

A group of parents-who are member of the high school's PTC-meet in secret. These are no ordinary townsfolk; the parents worship Black Magic. The PTC members tell Jim Ausbury that they were responsible for Shannon's death. Anxious for the police and FBI investigations to end, and realizing that Shannon makes the perfect scapegoat, they fabricate a story in which Shannon killed Jerry out of jealousy. But Jim Ausbury, disillusioned with his religion and disgusted with the PTC members and their lie about his daughter, tells Mulder the truth -- Shannon and other youngsters were forced to participate in the ancient rituals against their will. Using post hypnotic suggestion, the memory of the rituals was repressed. After exposing the conspiracy, Ausbury is attacked and swallowed by a large python.

Recalling that Mrs. Paddock kept a snake in her room, the agents decide an investigation is in order. But when they arrive at the school, PTC members take them hostage. Before the occultists can do the agents harm, they suddenly and mysteriously attack and kill one another. Mulder and Scully escape and search unsuccessfully for Mrs. Paddock.