Eighteen-year-old Cady Eastman has spent nearly every summer of her life on the private island of Beechwood, near Martha’s Vineyard, along with the rest of the wealthy Sinclair family. The summers of Cady’s childhood were uneventful, as she played with her two cousins, Johnny and Mirren. Everything changes during Year Eight, however, as Cady’s aunt Carrie brings her boyfriend Ed and his nephew Gat. Gat is about the same age as Cady, Johnny, and Mirren, and the four become fast friends, calling themselves “the Liars”; Cady and Gat also eventually fall in love and begin to spend more time alone together during their teenage years. However, while Gat—who is South Asian and therefore an outsider in this Old New England family—is superficially welcomed into the family, it is clear that the budding romance between him and Cady creates tension among the Sinclairs, especially for the patriarch of the family, Harris.
The Sinclairs are an old New England family: Harris and Tipper have three daughters, Penny, Carrie, and Bess, each of whom has a large house on Beechwood island and an enormous inheritance. The Sinclair clan attempt to maintain a façade of absolute perfection, but as Cady notes at the beginning of the novel, that image is built on lies and fantasy. Beneath the surface, the Sinclair sisters are deeply dependent on their father, needing both his money and his approval to survive. The insular family structure is overwhelming to outsiders, and on the day that Cady’s father decides to leave her mother, he notes that he cannot stand the pressure of being a Sinclair any longer. In fact, all of the sisters’ marriages end in divorce, and when Carrie brings Ed to the island, Harris is reluctant to accept him as one of the family. While Harris pays lip service to equality and considers himself educated and enlightened on social matters, his reaction to Gat’s racial difference reveals a surprising degree of bigotry. He is happy to vote for Barack Obama yet is unwilling to accept that his granddaughter is in love with a South Asian man.
Any semblance of family harmony is dissolved when Tipper Harris dies, leaving Bess, Carrie, and Penny to argue over their relationship with their father and, more importantly, his vast fortune. Each of the women believes that she is owed a larger share of the inheritance, and they even involve their children—Johnny, Mirren, and Cady—asking them to lobby Harris for more money or prized possessions. The Sinclair sisters depend heavily on this money, as none of them are able to support their families on their own: Penny’s job breeding dogs brings in very little money, Carrie’s jewelry boutique was a failure, and stay-at-home mom Bess has no income of her own. To make matters worse, Harris often pits the women against each other in order to maintain control over their lives.
The summer that Cady is fifteen years old, she is involved in some kind of accident that lands her in the hospital with a serious head injury, with no memory of exactly what happened to her. She recalls waking up on the beach but has no idea how she got there; when she asks about the accident, she gets no concrete answers and is continually frustrated by her mother’s refusal to tell her the whole story. Cady spends two years recovering from her injuries, suffering from chronic migraines and wondering helplessly what happened that night on Beechwood. Instead of returning to the island the following summer, Cady is forced to travel to Europe with her father, Mr. Eastman. She misses the rest of the Liars—Johnny, Mirren, and Gat—and writes to them constantly; she never hears back from any of them, which leaves her confused and sad.
The summer she turns seventeen, Cady returns to the island with her mother, and is elated to be reunited with her closest confidants—especially Gat, who is still deeply in love with her. Due to the constant infighting among the adults, the Liars isolate themselves in a house on the far side of the island, and Cady and Gat continue their teenage romance away from the prying eyes of their parents. A number of things have changed while Cady was away, but the most disturbing is the drastic change to Clairmont, the main house on the island: Harris made extensive renovations to the charming old house, turning it into something modern, austere, and antiseptic, and re-named it New Clairmont.
While she is glad to be back with her family for the summer, Cady is intensely focused on finding out what happened on the night of her accident—she asks everyone in her family, but they have all been advised not to tell her anything, and to let her recover those memories on her own. Frustrated but determined, Cady maps out all of the clues to that night on the wall of her bedroom, like a detective working to solve a crime.
With the help of Johnny, Mirren, and Gat, Cady eventually begins to recall the events leading up to the accident. She learns that years earlier, Ed had proposed to Carrie but that Carrie had refused, fearing that she would lose her inheritance if she married an Indian man. Cady also recalls the anger with which she and the other Liars discussed their plan to destroy Clairmont, the big house on the island that—to them, at least—represented the bigotry and greed that was tearing apart their family. They had decided that without Clairmont and all the valuable possessions inside it, the Sinclair sisters would no longer have anything to feud over. Finally, Cady’s memories of that fateful night return to her: how they forgot to let the dogs out of the house before setting it on fire, how they each took a different part of the house, and how the fire spread more rapidly than they expected, trapping Johnny, Mirren, and Gat in the building, killing them.
It is only when Cady has recovered the memories of the accident, and her role in the deaths of her closest friends, that she realizes that she has been spending the summer with the ghosts of Johnny, Mirren, and Gat. She speaks with them one more time to say goodbye, and they disappear forever. Grief-stricken but ready to heal, Cady returns to the rest of her family in New Clairmont.
