Laura Hall, separated from her husband, Richard, commits suicide after Richard informs her he plans to marry Grace Marshall, a woman he met while researching a book about an extremist Christian cult. Raised in the cult, Grace was the sole survivor of their mass suicide, led by her father. Laura’s death devastates her and Richard’s children, teenage Aidan and young Mia. Six months later, Richard announces that they will spend Christmas with Grace at the family’s remote Massachusetts lodge to get to know each other. Aidan and Mia uncover Grace’s past, including video footage of the cult, showing the deceased followers draped in purple silk with duct tape across their mouths reading “sin.” At the lodge, the children act hostile toward Grace and refuse efforts to bond with her, even after Richard departs back to the city for a work obligation. Grace’s unease is compounded by the abundance of Catholic iconography in the cabin, which causes her to have nightmares about her father. After being reprimanded for watching her shower, Aidan prepares Grace a cup of cocoa.