Shirley Jackson is probably best remembered for “The Lottery” and The Haunting of Hill House, but her 1962 gothic mystery We Have Always Lived in the Castle is widely regarded as her greatest literary achievement. Published three years after The Haunting of Hill House—and just three years before Jackson’s untimely death—We Have Always Lived in the Castle is an eerie, elegant masterpiece that forever cemented its author’s reputation as the grande dame of macabre fiction.

The story centers on Merricat and Constance Blackwood, two sisters who live with their ailing uncle on their family’s sprawling Vermont estate. The three Blackwoods used to be seven, but tragedy befell the clan six years earlier, when the sisters’ parents, their younger brother, and an aunt died after someone slipped arsenic into the family’s sugar bowl. Constance was tried and acquitted for the murders, but the surviving Blackwoods are reviled by their neighbors and live in isolation. That is, until a cousin, Charles, shows up and installs himself in the household. Constance is taken with Charles, but Merricat suspects him of sinister intent. His presence slowly destabilizes what remains of the family until disaster strikes once again.

We Have Always Lived in the Castle is a master class in mystery and ambiguity, and answers to some of the book’s central questions are teased rather than spelled out. Here are nine spoiler-free facts that might enhance your next (or first) reading of Jackson’s disquieting classic.

1. We Have Always Lived in the Castle was inspired by the unsolved poisoning death of an English lawyer.

Charles Bravo died of antimony poisoning in April 1876, just four months after his wedding. The still-unsolved case was a media sensation in Victorian England, and everyone had a theory. Depending on whom you asked, Bravo either died by suicide or was murdered by his wife, or maybe his wife’s former lover, or perhaps his housekeeper—that is, unless he accidentally poisoned himself while trying to poison his wife. In her exhaustively researched 2016 biography Shirley Jackson: A Rather Haunted Life, Ruth Franklin asserts that Jackson was inspired by the case when she began writing We Have Always Lived in the Castle.

2. Shirley Jackson worried that We Have Always Lived in the Castle was “as unoriginal as an old sponge.”

According to correspondence reviewed by Franklin, Jackson struggled with early drafts of We Have Always Lived in the Castle. In letters to a friend, Jackson called it “a perfectly splendid book” that had one glaring problem: “everything in it has been done before.” Fortunately, Jackson recognized her early trials with the book as the same sort of rocky beginning that usually characterized her writing process, and she pushed on.

3. The main characters are loosely based on Jackson's daughters, Sarah and Joanne.

According to Franklin’s book, Jackson told her older daughter, Joanne, that Constance and Merricat were loosely modeled on Joanne and her sister, Sarah. Sarah, who was 12 years old when Jackson began revising We Have Always Lived in the Castle, read the manuscript while her mom worked on it, sometimes offering suggestions that Jackson incorporated.

It’s also not hard to see reflections of the author in the two characters. In her 1988 biography Private Demons: The Life of Shirley Jackson, Judy Oppenheimer identified Constance and Merricat as “the yin and yang of Shirley’s own inner self.” In 2018, Jackson’s son, Laurence Hyman, said, “I think that my mother really put herself into [We Have Always Lived in the Castle] in a way that she may not have in some of the others.”

4. The sisters were originally named Constance and Jenny, and they were plotting to murder Jenny’s husband.

Jackson changed the story out of concerns that readers would mistakenly assume one or both of the sisters were lesbians. Such an interpretation, Jackson feared, would cause readers to misunderstand the story and overlook its themes.

5. We Have Always Lived in the Castle needed virtually no major edits.

Unfortunately, one of the few changes made to Jackson's manuscript resulted in an error: On page one, "death-cap” mushroom was changed in copy editing to "death-cup” mushroom, which is not a thing.

6. Jackson didn't think We Have Always Lived in the Castle would be a success.

The author thought We Have Always Lived in the Castle, with a first edition that clocked in at a slim 214 pages, was too short, and that the pre-publication praise she received was “the kiss of death on any book.” According to a letter Jackson wrote to her parents, she also thought the heroine, Merricat, was a bit on the “batty” side.

7. Upon its release, critics praised We Have Always Lived in the Castle as Shirley Jackson’s masterpiece.

According to Franklin, critics “were virtually unanimous” in their praise for We Have Always Lived in the Castle. Orville Prescott, writing for The New York Times, called Jackson “a literary sorceress of uncanny prowess,” while others compared her to Dostoyevsky and Faulkner. In her short but enthusiastic review for Esquire, Dorothy Parker called the novel a “miracle,” writing that it “brings back all my faith in terror and death. I can say no higher of it and her.”

8. We Have Always Lived in the Castle marked the first and only time Jackson would see her name on The New York Times Bestseller list.

We Have Always Lived in the Castle was published in September 1962; by late November, Franklin writes, “close to 30,000 copies had been sold.” It hit The New York Times bestseller list in December and remained there until early 1963. For comparison, Jackson’s previous novel, The Haunting of Hill House, had sold about 12,000 copies in its first six months of publication.

9. We Have Always Lived in the Castle was Jackson's last finished novel.

Jackson’s follow-up to We Have Always Lived in the Castle was to be Come Along With Me, a decidedly more cheerful novel about a middle-aged woman who reinvents herself as a spirit medium after the death of her husband. Jackson had written 75 pages of it by August 8, 1965, when she died in her sleep at the age of 48.

10. It took 56 years for We Have Always Lived in the Castle to make it to the big screen.

Jackson’s agent sold the dramatic rights to We Have Always Lived in the Castle for a respectable $10,000 before the author’s death, and a stage adaptation made it to Broadway in 1966. But it wasn’t until 2018 that the book was finally adapted for the screen. According to an interview at the film’s premiere, Jackson’s son, Laurence Hyman, worked closely with director Stacie Passon, and he was pleased with the final product. Regardless of whether you share Hyman’s assessment of the film, we can all agree that the casting of Crispin Glover as the unhinged Uncle Julian was nothing short of inspired.