After suffering a traumatic brain injury from a car accident, Mary Dunn begins to believe that her husband Grayson has been replaced by an impostor. She receives phone calls from an unknown number with a voice that claims to be the “real Grayson.” Mary starts to suspect that she’s living in a parallel universe filled with impostors who are gaslighting her and keeping her against her will. She's also haunted by a gruesome presence that makes her question her own sanity. The “real Grayson” tries to convince her to move on with her life and accept her new reality, but Mary can’t let go of the feeling that she's not safe and becomes hostile. Tensions reach a breaking point when Mary finds out she is pregnant with the supposed impostor’s baby.