The following version of this book was used to create the guide: Habeck, Emily. Shark Heart: A Love Story. Simon & Schuster, 2023. Paperback edition.

Lewis and Wren meet when she is at the same restaurant where he is on a date with another woman. He walks the woman to the car and then goes back in to meet Wren. The two fall in love. Lewis previously lived in New York to pursue an acting career, but he moved back to Texas when he was not able to break into the business. Here he works as an acting teacher and finds satisfaction and fulfillment in this job. Wren works in finance and is fairly alone in life. She likes the world of finance because numbers are predictable and she builds her life around lists and the predictable. The two get married.

Shortly after they are married, Lewis gets the diagnosis that he has a genetic mutation and will, within less than a year, transform into a great white shark. He keeps the news to himself for a brief time while he adjusts to it, but soon he tells Wren of his fate. Taking care of someone mutating into a shark can be dangerous, but she does her best to care for him. She buys ever larger quantities of fish for him and tries to make him comfortable in the bathtub. Eventually she buys a pool for him to sleep in. Lewis’s transformation is both physical and psychological. He is kicked out of the zoo for pounding on the underwater exhibits. He tears his house apart at one time. Eventually he attacks the man who was his replacement at his school, and they are given only three weeks to release him into the ocean or the government will do it for him.

During the time of Lewis’s transition, Wren meets somebody she refers to as the Tiny Pregnant Woman. She meets this woman at the pool and learns that the woman is pregnant with twin baby falcons. This pregnancy is very dangerous because the birds will likely see her as an egg and attempt to peck their way out of her body. Wren and the Tiny Pregnant Woman part ways eventually, but she later looks up the woman only to find her obituary. She did, indeed, die because of her pregnancy.

Wren slowly drives Lewis to the coast. Because she is imminently practical and tries to prepare for every situation, she decides to buy scuba gear before they head to the coast. This way she and Lewis can still be together. Lewis knows that he cannot keep her safe and that they must part. He swims away. Wren waits for him all night, but when he does not return, she knows that he is gone for good. She has an affair with a man in his truck, and then she slowly heads home to rebuild her life.

The narrative moves to that of Angela, Wren’s mother. Angela grows up largely alone due to a father who works too much and a mother who drinks too much. She starts staying with a boy named Marcos on his houseboat when she is a young teenager. She eventually becomes pregnant by him. When they need more money, Angela gets a job at a motel where she meets Julia and her brother, George. George eventually falls for Julia. Marcos gets jealous at one point and makes Angela quit her job. He is abusive, and when he breaks a bone of hers, she leaves him and goes to live with Julia’s family. Eventually she goes back to Marcos, but he leaves both her and their daughter Wren to pursue a life elsewhere. She enters into a relationship with George, but she leaves him when she gets the diagnosis that she will turn into a Komodo dragon. She does not want to tie him to this fate.

Angela’s mutation is a slow process that will take up to 20 years. Wren has to take care of her mother as Angela turns less and less human. Eventually Angela has to live in a facility when her transformation is near complete. During this time, Wren goes away to college. There she has a romance with another woman. This romance ends, however, as Wren cannot open herself up to a relationship with this woman. The other woman, Rachel, leaves her.

Back in the ocean, Lewis mourns the loss of Wren and wishes he had not swam away. He eventually befriends another shark that was once human. He does not particularly like this shark, and they part ways. He contemplates suicide at one point, distraught at his fate, but ultimately he decides to embrace his new life and he and Margaret, the other shark, make a life built around stories and their friendship. Back on land, Wren finds out she is pregnant with Lewis’s baby, and she names her baby Joy. While raising Joy she is able to rebuild a life and find happiness despite having lost Lewis and many of the other people she loved in life.