Merricat lives with her sister Constance and her Uncle Julian. The trio are survivors of an arsenic poisoning that killed everyone else in the family five years prior. Merricat is bold and imaginative, and protects the property with "spells". Despite being hated by the townspeople, the sisters live an idyllic life, until cousin Charles arrives.
Charles offers to help around the house, and inquires about the family's finances. Constance is charmed by Charles, and Merricat resents Charles' intrusion. As Charles and Merricat battle for control, tragedy threatens to strike again.