In a small suburban neighborhood, a mother finds her dog's mutilated body strung across the lawn. Meanwhile, a slideshow of Brigitte (Emily Perkins) and Ginger Fitzgerald (Katharine Isabelle) creating staged deaths for a school project plays in their classroom. Their teacher and the school's guidance counselor, Mr. Wayne, (Peter Keleghan) demands to see them after class. Later, they smoke cigarettes and play "Search and Destroy" on the school's game field, dissing people they dislike, and imagining how they may die. Trina Sinclair's (Danielle Hampton) friend overhears Brigitte describing Trina's character and death, and tells Trina. The sisters notice this, and Ginger tells Brigitte she will "cover her" in the game. However, as Ginger is distracted, Trina pushes Brigitte into the remains of a dog, a victim of the Beast of Bailey Downs, a wild animal which has been killing pet dogs. Together, Brigitte and Ginger decide to kidnap Trina's dog that night, and imply that the Beast of Bailey Downs killed it.They set out and find the mutilated corpse of another dog. They decide to take it with them to convince Trina it is actually her dog, but, as they pick it up, a leg comes off in Brigitte's hand. Brigitte notices blood on Ginger, thinking it is from the dog, but it proves to be from Ginger's first period. The Beast of Bailey Downs attacks, and drags her into the woods screaming. Brigitte rescues Ginger. As the sisters flee, they narrowly escape being hit by an approaching van driven by Sam (Kris Lemche), which hits and kills the Beast. Brigitte finds Ginger's wounds are already healing and begs her to go to a hospital. Ginger refuses, as she does not want their mother (Mimi Rogers) to find out. After a few days, Ginger begins to grow hair from her wounds, sprouts a tail and menstruates heavily. A rift forms between the sisters after Ginger smokes marijuana with Jason, and aggressively pursues him. Ignoring Brigitte's warnings, she has unprotected sex with Jason, then kills a neighbour's dog.Frightened by what is happening to Ginger, Brigitte turns to Sam. Agreeing the Beast of Bailey Downs is a lycanthrope, he suggests a pure silver ring may cure Ginger. Brigitte persuades Ginger to have her navel pierced using the ring, but it is ineffective.Later, Trina goes to the Fitzgerald house claiming Ginger kidnapped her dog. As Ginger and Trina fight, Trina slips, hitting her head on the corner of the kitchen counter, and dies. The sisters panic, narrowly avoiding their parents seeing them as they put the body in the freezer, explaining the blood to be part of another series of death photos for the school project. Brigitte later accidentally breaks off two of Trina's fingers trying to get the corpse from the freezer. As they take Trina's body to bury it, they lose the fingers. Brigitte tells Ginger she cannot go out anymore, but Ginger remains defiant.On the pretence that Brigitte is the one "changing" instead of Ginger, they visit Sam, who suggests a monkshood solution for Ginger's illness; and informs them that the monkshood grows everywhere, however it only grows during spring. Ginger angrily tells him that they have no time, and accuses him of just wanting to have sex with Brigitte before storming out.On Halloween, Brigitte takes her mother's monkshood, which was purchased from a craft store, and asks Sam to make the cure. Sam warns her asks if it is for Ginger. Brigitte admits the truth, and promises to go to the Greenhouse Bash party.While trying to track down Ginger, Brigitte is attacked by Jason (whom Ginger infected through unprotected sex) and she defends herself by using the cure on him. She witnesses his immediate change in behavior, which proves the cure's success.Ginger returns to school looking for Jason. As Brigitte arrives, a message on the PA asks her to go to the Guidance office. She knocks, and is dragged inside by Ginger who has killed the counselor. Brigitte calms Ginger down, and goes to find cleaning supplies, but returns to see the janitor with his throat torn open. He survives, though infected, until Brigitte says he should have gotten help, which incites Ginger to disembowel him with her hand.The sisters' mother discovers Trina's corpse, and goes looking for her daughters. While she is looking for her daughters, she sees Brigitte running, and picks her up. As she drives Brigitte to the Greenhouse Bash, she tells her that she will burn the house down by letting it fill up with gas then lighting a match to erase evidence of Trina's death, and their escape. Brigitte arrives to find Sam rejecting Ginger's advances. As he approaches Ginger, she breaks his arm. In despair, Brigitte infects herself as Sam pleads with her not to. As the sisters leave, Sam knocks Ginger out with a shovel. Brigitte and Sam then take her back to the Fitzgerald house in his van, and prepare more of the cure for Ginger.Ginger fully transforms into a werewolf on the way home and escapes the van. Afraid, and unaware she has transformed, Sam and Brigitte hide in the pantry, and he makes the solution. As he goes to find Ginger, Ginger-Wolf mutilates Sam. Brigitte picks up the dropped syringe, and follows the blood trail downstairs. She tries to drink Sam's blood in an attempt to calm Ginger-Wolf, but chokes on it. Ginger-Wolf senses Brigitte's insincerity and kills Sam in front of her, then leaps at Brigitte. As Ginger-Wolf stalks Brigitte through the basement, Brigitte returns to the room where they grew up, finding the knife that Ginger had been using to remove her tail. Brigitte holds the cure in one hand and the knife in the other. Brigitte is told to leave but refuses, only to infuriate Ginger-Wolf, resulting in Ginger-Wolf lunging at Brigitte who stabs her with the knife, instead of the cure. As the movie ends, Brigitte lays her head upon Ginger-Wolf, sobbing, listening until its breathing finally stops.