After Lisa’s father dies in a hit-and-run accident, it is revealed that he had a hidden daughter from his first marriage. This daughter, named Marie, is a convicted murderer who has been released from prison early and is consumed by a desire for vengeance. Assuming a new identity as Bethany, Marie has cunningly positioned herself close to Lisa, both in residence and employment, all the while plotting her retribution for the life she believes was unjustly denied to her—a life she thinks their father wrongfully bestowed upon Lisa. Marie has devised a lethal scheme to reclaim what she believes is rightfully hers, forcing Lisa, her mother, and their friends into a desperate struggle for survival against the murderous sister they never knew existed.