We have always lived in the castle

Six years after four members of the Blackwood family died of arsenic poisoning the three survivors—elder agoraphobic sister Constance; wheelchair-bound Uncle Julian; and 18-year-old Mary Katherine or Merricat—live in peaceful solitude. Merricat has devised an eccentric set of laws and defensive charms to keep the estate safe from intruding villagers. However a stranger appears one day—cousin Charles who is after the Blackwood fortune—and manages to infiltrate their carefully guarded lives. Merricat resorts to severe measures after failing to elude him through polite or occult means resulting in crisis tragedy and the disclosure of a dreadful secret.