A young woman named Lucie starts training as a caregiver for the elderly in a remote French coastal town. One day, Lucie and her colleagues visit Mrs. Jessel, a comatose former dance teacher who resides in a sprawling, decrepit mansion filled with eerie artifacts. During the visit, Lucie learns of a hidden treasure rumored to be concealed within the mansion's walls. Driven by curiosity and the allure of wealth, she decides to return with her friends Ben and William to search for the treasure on Halloween night.

As they infiltrate the dark, labyrinthine manor, the atmosphere becomes increasingly ominous. The friends soon discover that the house harbors sinister secrets and is imbued with malevolent supernatural forces. As they delve deeper into the mansion's mysteries, they encounter a series of terrifying events that challenge their sanity and survival.