Black Mountain National Park is steeped in mystery, with a history of livestock vanishing after straying onto the mountain and bizarre incidents of local residents disappearing and reappearing. Among these mysteries is the case of the Wahldrov family, who vanished without a trace. Cassian Wahldrov comes back to Black Mountain after his autistic younger brother, Manny, goes missing. He and his sister, Mae, embark on a quest to locate him. However, their search is soon thwarted by an eerie force that separates them and gradually unravels their efforts.