Black Mountain National Park has a long, strange history: from masses of missing livestock wandering onto the mountain to unusual disappearances and reappearances of local townsfolk, including members of the entire Wahldrov family. After the disappearance of autistic younger brother Manny, Cassian Wahldrov returns home to Black Mountain to search for him together with his sister Mae. Their efforts are quickly overshadowed by a strange force that both splits them up and slowly picks them apart.