Occult-obsessed teenager Leah Reyes interrupts her mother in the midst of an emotional breakdown to remind Mrs. Reyes that she is attending a book signing with her friends Janice, Aaron, and Rob. At the signing, Leah meets occult expert Rowen Dove, author of the book "Black River, Black Magic."Still grieving the death of Leah's father and hoping for a fresh start, Mrs. Reyes informs Leah that they are moving to a remote woodland home at the end of the month. The news deepens growing discord between mother and daughter as Leah worries about transferring to a new school and losing her friends.Shortly after moving in, frustration between the two women boils over into a fight during which Mrs. Reyes insults Leah and calls her friends losers. Wishing her mother was dead, Leah gathers items according to an occult manual and performs a blood ritual in the woods to summon the witch's familiar Pyewacket.Mrs. Reyes cleans Leah's deep arm wound after seeing her daughter bleed at the dinner table. Mrs. Reyes apologizes for her earlier outburst.The next day, Leah finds the front door open and dirt on the floor of the house. Leah's guilt over using black magic to curse her mother grows when they continue making amends during a daytime trip into town.Leah begins believing the ritual worked after Mrs. Reyes nearly crashes their car on the drive home. Mrs. Reyes apologizes once more for saying awful things to Leah the previous day.Leah is woken by the sounds of footsteps in the attic. Leah wakes Mrs. Reyes to investigate, but they find no one upstairs.A shadowy figure manifests in Leah's bedroom while she sleeps. Leah wakes in the forest to find that her arm wound reopened.Leah tells Janice, Aaron, and Rob about the strange activity she has witnessed since summoning Pyewacket. Rob berates Leah for using black magic to try killing her mother. Janice tells Leah she wants to see what is happening firsthand.Janice comes to the house for a sleepover. Janice jokingly pretends to become entranced when the two girls explore the woods in the dark.Mrs. Reyes wakes Leah the next morning to tell her that Janice is missing. They find Janice locked inside Mrs. Reyes' car crying and demanding to be taken home. Janice stops attending school and refuses to tell Leah what happened to her.Leah contacts Rowen Dove for help. Rowen explains that after fulfilling its function, Pyewacket will go after the person who summoned it. Rowen advises Leah to perform the summoning ritual in reverse in order to undo the curse before Pyewacket can take her mother. Rowen further warns that the manipulative entity can take many forms, so Leah should not trust anything she sees.Leah gathers the necessary items and returns to the woods to redo the ritual. Leah hears her mother calling for her from the house at the same time she discovers Mrs. Reyes' dead body lying on the forest floor. Leah calls 911 to report her mother's apparent death. Leah then calls Aaron to come and get her. The body in the forest seemingly begins to reanimate.A text message from Aaron summons Leah back to her house. When she gets there, Leah does not find Aaron, but confronts a vision of her mother that morphs into Pyewacket and attacks. Leah escapes to the attic.Mrs. Reyes finds her daughter cowering in the attic with a knife. Although Leah is uncertain of her mother's true identity, Mrs. Reyes convinces Leah to relinquish the blade.Convinced her mother is Pyewacket in disguise, Leah douses Mrs. Reyes in gasoline and burns her alive in her bed. Aaron arrives to find the house engulfed in flames and Leah collapsed on the ground outside.Leah recovers in a police station. A detective informs Leah that they never found a body in the woods, only Mrs. Reyes' charred corpse in the house. The detective resumes questioning Leah as a suspect in her mother's murder.