In 1992, young Rebecca ventures to her family’s pool one evening to retrieve a toy boat belonging to her terminally ill brother, Tommy. As she reaches for it, something drags her beneath the water’s surface.
Fast forward to the present day, the Waller family—Ray, Eve, and their children Izzy and Elliot—are on the hunt for a new home following Ray’s retirement from baseball due to illness. Intrigued by the prospect of a house with a pool, which might aid Ray’s condition, they settle on a property boasting such a feature. However, Ray sustains a minor injury while tending to the pool, revealing its unique self-sustaining nature fed by an underground spring.
As Ray immerses himself in pool therapy, his health miraculously improves. Yet, Eve grows increasingly uneasy about his transformation. Disturbing incidents unfold, with both Izzy and Elliot experiencing attacks within the pool, and even their pet cat vanishing. During a fateful poolside gathering, their realtor divulges the tragic history of the previous owners, including the drowning of Rebecca Summers, the previous owner’s daughter.
Driven by concern and curiosity, Eve delves into the dark past of the house, meeting Lucy, Rebecca’s mother. Lucy reveals a chilling truth: the pool’s waters hold a malevolent entity demanding sacrifices for its healing powers. Appalled, Eve realizes that Ray’s recovery comes at a terrible cost—the life of one of their children.
Returning home, Eve confronts the horrifying reality that Ray is under the entity’s control, endangering their children. In a desperate bid to save them, a harrowing showdown unfolds, with Izzy bravely facing the entity inhabiting her father. Eve rescues Elliot with Rebecca’s spectral guidance, while Izzy’s actions help Ray regain control momentarily. Tragically, Ray ultimately sacrifices himself to the entity to protect his family.
Determined to prevent further tragedies, Eve, Izzy, and Elliot decide to remain in the house, opting to fill in the pool to prevent further loss. In a somber resolution, they vow to ensure no one else falls victim to the pool’s sinister influence.