We Have Always Lived in the Castle by Shirley Jackson

Living in the Blackwood family home with only her sister Constance and her Uncle Julian for company, Merricat just wants to preserve their delicate way of life. But ever since Constance was acquitted of murdering the rest of the family, the world isn't leaving the Blackwoods alone. And when Cousin Charles arrives, armed with overtures of friendship and a desperate need to get into the safe, Merricat must do everything in her power to protect the remaining family. 

In her final novel, Shirley Jackson displays a mastery of suspense, family relationships and black comedy.