Set in 1967 Los Angeles, widowed mother Alice Zander struggles to support her two daughters, teenager Doris and precocious younger sister Lina, by posing as a fraudulent medium. Conducting elaborate séances from their suburban home, Alice uses hidden gimmicks to comfort grieving clients. Seeking to boost their struggling business and connect with her late husband, Alice purchases a Ouija board, inadvertently introducing a malevolent supernatural element into their household.Doris, grieving her father deeply and feeling isolated, begins experimenting alone with the board outside of the routine parlor tricks. Drawn to the artifact, she makes contact with a lingering entity that she believes is her benevolent father. However, the spirit is actually a pack of ruthless demons. The entity rapidly possesses Doris, granting her supernatural strength, the ability to write in Polish automatically, and a chilling knack for manipulating sewing threads and human voices.Initially, Alice and Lina are stunned by the sudden success of their séances, as the possessed Doris legitimately channels the dead with eerie precision, attracting the attention of wealthy clients. Father Tom, the principal at the girls' school, visits the home to investigate the phenomena and offers guidance. However, Lina soon discovers the horrific truth: the board’s warning letters spell out a terrifying message revealing that the entity has tricked them all. Lina uncovers the dark history of the house, realizing that a former sadistic doctor previously used the basement to
torture and murder deaf patients, and these vengeful spirits now inhabit Doris.As the demonic infestation escalates, the entities brutally attack and murder Father Tom, dragging him into the cellar. Alice is captured by the possessed Doris, who subjects her to psychological torment, stitching her mouth shut to permanently silence her. Lina fights desperately to save her remaining family, battling the supernatural forces tearing their home apart. In a harrowing confrontation, Lina manages to stab the board, intending to break the connection. Recognizing that Doris’s body is too thoroughly corrupted to survive
the possession, a grief-stricken Alice intentionally allows the demon to switch targets to her, choosing to die so her daughter might be freed. In the ensuing chaos, Lina manages to drive a blade into Doris, severely weakening the primary spirit, but too late to save Alice. Sometime later, a traumatized Lina resides in a psychiatric hospital, where she ruthlessly murders a nurse who doubts her, proving the evil within her family line is far from extinguished.