Fifteen-year-old Brigitte Fitzgerald (Emily Perkins) and her nearly-sixteen sister Ginger (Katharine Isabelle), are a team – best friends and self-styled outcasts. Obsessed with dying and bound by a childhood pact to stay together forever, they loathe their mind-numbing existence in the suburb of Bailey Downs. On the night of Ginger’s first period, the two girls are heading through the woods on the edge of the suburb to pull an evil prank on an obnoxious classmate when Ginger is savagely attacked by a wild creature.
Ginger survives as her horrible wounds miraculously heal over, but something is not quite right. Ginger is irritable and in denial. But to Brigitte it is obvious that a terrifying force has taken hold of her sister. She’s convinced that the hairs growing from Ginger’s scars and the tail emerging from the base of her spine can mean only one thing – Ginger is becoming a werewolf.
Driven by a mounting, inexplicable blood lust, Ginger transforms from a disdainful outsider into an aggressive young woman on the prowl. Afraid to tell anyone of her suspicions yet desperate to save her sister from the infection which is slowly overtaking her, Brigitte has no where else to turn except to enigmatic bad-boy Sam, the local pot supplier and amateur botanist. Together they search for a way to cure the otherworldly infection coursing through Ginger’s veins.
Ginger’s slow, horrifying transformation coincides with her battle with her rationality as she alternately pleads for Brigitte’s help and jealously accuses her of betrayal. Ginger’s savage behaviour escalates. As Brigitte strives to protect Ginger, she becomes complicit in her violent, uncontrollable crimes.
On Halloween night, a violent struggle between Brigitte, Sam and Ginger leaves Brigitte with little choice but to put an end to the nightmare which started 28 days earlier deep in the woods one night.