During a family vacation to Santa Cruz, Adelaide Wilson is haunted by an unresolved trauma from her past. As a child, she encountered a doppelgänger of herself in a beachside funhouse, an experience that left her scarred and cautious. Now, as an adult, she revisits the beachfront home where she grew up, along with her husband Gabe, daughter Zora, and son Jason. Amidst her increasing anxiety and the family's attempts to enjoy their summer getaway, Adelaide remains fixated on the chilling feeling that something terrible is going to happen to her loved ones.

One night, the Wilsons are confronted by a group of menacing figures dressed in red, standing hand in hand in their driveway. The eerie strangers break into the Wilsons' home, revealing themselves to be uncanny duplicates of each family member. These doppelgängers exhibit twisted behaviors and possess knowledge of their counterparts' lives. The Wilson family is thrown into a desperate struggle for survival as they attempt to understand and outwit these mysterious, malevolent doubles, while the larger scope of these strange events begins to unfold beyond the confines of their immediate ordeal.