A dead body is found and Catherine "Kya" Clark is accused of murder.Kya's story begins when she lives in a shack with her poor family in a North Carolina marsh in 1953. As their abusive alcoholic father gambles their money away, Kya's mother and older siblings flee one by one, leaving Kya alone with him until he too abandons her at the age of seven. She survives by selling mussels at Barkley Cove's general store. The townspeople know her as the "Marsh Girl".Over the years, her slightly older friend Tate Walker lends her books and teaches her to read, write, and count. They share an interest in nature and begin a romantic relationship until Tate leaves for college and breaks his promise to return to her on the 4th of July.In 1968, Kya begins a relationship with popular local quarterback Chase Andrews, who promises her marriage. Chase gives Kya a small shell which she makes into a necklace and gives to him. A year later, Tate returns to Barkley Cove wanting to rekindle their romance, but Kya is unsure. Kya ends her relationship with Chase when she discovers he is already engaged to another girl.Kya has her nature drawings and writings published and the income helps her keep her home. Her older brother Jodie reappears and tells her their mother died before she was able to reunite her children. Jodie promises to visit when he can.Kya rebuffs Chase's persistent attentions and successfully fights off his rape attempt, vowing to kill him if he does not leave her alone. The threat is overheard by a fisherman. Chase returns and vandalizes Kya's home while she hides in the bushes. Days later, Chase is found dead at the bottom of a fire tower from which he had apparently fallen. The muddy bog floods at high tide, destroying any tracks from the killer, and no fingerprints are found in the tower. The shell necklace, which he had been wearing on the evening of his death, is missing from his body. Kya is charged with first-degree murder and prejudged by the suspicious townspeople.Despite knowing Kya had been meeting with a book publisher in Greenville at the time, the police and the prosecutor speculate she could have disguised herself and made an overnight round-trip bus ride to Barkley Cove, lured Chase to the fire tower during the brief layover and killed him. With only the unfounded theory, the missing necklace, and the fisherman's testimony, Kya is found not guilty at her 1969 trial.Kya and Tate spend the rest of their lives together. Kya publishes illustrated nature books, and is frequently visited by Jodie and his family. While boating through the swamp in her 70s, she imagines seeing her mother returning to the cabin. Tate finds Kya lying dead in the boat at their dock. Boxing up Kya's things, Tate finds a passage in her journal saying that to protect the prey, sometimes the predator has to be killed. It is accompanied by a drawing of Chase. Next he finds the missing shell necklace. Tate throws the necklace into the marsh water.