We Have Always Lived in the Castle is the surreal story of teenage Merricat and her older sister Constance, who live with their aging uncle in a mansion on the outskirts of a small town. Years earlier, the rest of their family was poisoned, and most people think Constance is responsible; consequently, the sisters are shunned and do their best to avoid society. However, when their cousin Charles comes to town, Merricat fears that everything may change. This novel explores the themes of family, isolation, and otherness.
The theme of persecution of people who exhibit "otherness" in small-town New England, by small-minded villagers, is at the forefront of We Have Always Lived in the Castle and is a repeated theme in Jackson's work. In her novels The Haunting of Hill House and, to a lesser extent, The Sundial , this theme is also central to the psychology of the story. In all these works, the main characters live in a house that stands alone on many acres, and is entirely separate physically, socially, as well as ideologically, from the main inhabitants of the town. In his 2006 introduction of the Penguin Classics edition, Jonathan Lethem stated that the recurring town is "pretty well recognizable as North Bennington, Vermont," where Jackson and her husband, Bennington professor Stanley Edgar Hyman, encountered strong "reflexive anti-Semitism and anti-intellectualism."
All of Jackson's work creates an atmosphere of strangeness and contact with what Lethem calls "a vast intimacy with everyday evil..." and how that intimacy affects "a village, a family, a self." Only in We Have Always Lived in the Castle , though, is there also a deep exploration of love and devotion despite the pervasive unease and perversity of character that runs through the story. Constance's complete absence of judgement of her sister and her crime is treated as absolutely normal and unremarkable, and it is clear throughout the story that Merricat loves and cares deeply for her sister, despite her otherwise apparently sociopathic tendencies.
The novel was described by Jackson's biographer, Judy Opphenheimer, as "a paean to agoraphobia," with the author's own agoraphobia and nervous conditions having greatly informed its psychology. Jackson freely admitted that the two young women in the story were liberally fictionalized versions of her own daughters. Written in deceptively simple language, by an entirely unreliable narrator, the novel implies that the two heroines may choose to live forever in the remaining three rooms of their house, since they prefer each other's company to that of any outsiders. Lethem calls this reversion to their pre-Charles stasis Merricat's "triumph."