Set in 1976, two young journalists leave for the French-Swiss border to report on a strange case of cattle mutilations for French TV. Accompanied by a team of forensic experts, they will go on to meet the scientific team delegated to follow the phenomenon. But they will soon be confronted with an unimaginable horror. As the team progresses, it becomes clear that the mountains hide a deadly secret and something terrifying is stalking them, intent on ensuring they never leave.