French teacher Clementine has recently moved into a large rambling house on the outskirts of Bucharest, Romania, with her student partner Lucas. One night the telephone rings with unintelligible voices on the line and they hear strange noises downstairs. Clearly not alone, a nightmare cat and mouse chase begins through all the empty rooms, out into the woods then far below them, as the terrified duo get relentlessly stalked by an unknown and unforgiving menace.