A year after a brutal home invasion that left her traumatized, Cecelia, along with her husband and their three-year-old daughter, move into a new house with a complex security system that is supposed to make her feel safe. But reality proves different as strange things begin to happen at home and the security system reveals that the house had a prior occupant: Lydia. On her quest to discover the fate of the mysterious Lydia, Cecelia realizes that that no one's secrets are safe, including her own.