Cadence, nearly eighteen, narrates her story in the first person. In Part One (“Welcome”), she describes the three generations of her family, the Sinclairs; Granddad, widowed; his three daughters, all divorced or separated from their husbands; and Cadence and her six cousins. The family spends every summer on a family-owned island. One aunt’s longtime boyfriend and his nephew, Gat, always join them there, even though Granddad doesn’t like the fact that they are of South Asian descent. Cadence, her two oldest cousins, and Gat are known in the family as “the Liars,” for unexplained reasons. Cadence and Gat fell in love when Cadence was fourteen, but the next summer there was an accident of some sort. Cadence doesn’t recall much, but apparently she suffered a head injury. She now has migraines, for which she takes prescription pain medication. None of the Liars stayed in touch with Cadence during her long recovery. The following summer, when her father took her on a trip to Europe, they didn’t reply to her emails.

In Part Two (“Vermont”), Cadence struggles to remember more of her accident. When she asks Penny for details, Penny replies tearfully that Cadence has asked many times before, and always finds the answers upsetting. When Cadence’s father wants to take her to Europe again next summer, Cadence insists on returning to the island. Her mother and father reluctantly settle on a plan for her to spend just the first month of the summer there. Meanwhile, it becomes clear during a visit from Granddad and a phone call with one of the younger cousins that all is not well with the family. Granddad’s mind is starting to fail, the younger cousins gossip about Cadence being a drug addict, and the cousin on the phone thinks the island is haunted.

Part Three (“Summer Seventeen”) begins with Cadence’s arrival at the island. To her shock, the old Victorian house where Granddad and Granny used to live has been completely rebuilt, as an unattractive modern structure. She reunites awkwardly with her aunts and the younger cousins, but her reunion with the Liars goes better, despite her resentment over not hearing from them in the last two years. The four Liars agree to stay together and not to spend much time with the rest of the family. Over the next week or two, Cadence begins to remember what happened two summers ago. Granddad and his daughters argued about the family home back in Boston. One aunt was resentful over the condition of her house on the island. Granddad also snapped at Cadence one day, about his right to do with his money as he pleased. In the present, Cadence makes progress reconnecting with the Liars, but they’re not very responsive to her questions about her accident.

In Part Four (“Look, a Fire”), Cadence starts to grasp what really happened. There had been an ugly showdown between Granddad and his daughters, about the division of the family inheritance. The fight ended with all four adults angrily leaving the island for a short time, taking the younger cousins with them. The Liars stayed behind. Since much of the family conflict had been about Granddad’s house and its contents, the Liars had deliberately burned the house down. Cadence is pleased that in the new house, Granddad and his daughters treat each other more kindly. Cadence’s feelings change, however, when she realizes that Granddad’s two dogs died in the fire. She and the other Liars are responsible for their deaths.

In Part Five (“Truth”), finally, Cadence confronts the whole truth: she alone survived the fire. The other three Liars died. They have spent the last few weeks with Cadence as ghosts, waiting for her to remember and understand. Now the Liars must leave. Cadence says final goodbyes to her two cousins and her beloved Gat. She carries with her the guilty knowledge of her role in their deaths. She is resolved to be kinder toward her surviving family from now on.