Shirin and her family are American Muslims. Her parents come from Iran, but she and her brother Navid were both born in the United States. Her parents move the family often in an ongoing effort to live in bigger homes in better neighborhoods to improve their opportunities for the future. As the story opens, Shirin and Navid are starting at a new high school for the third time in two years. Shirin is sixteen and a sophomore, while Navid, who is very protective of his sister, is a senior. A Very Wide Expanse of Sea tells Shirin’s story during that sophomore year.

A year has passed since 9/11, and because Shirin always wears a hijab, she is harassed and teased by other students. Once, just after the terrorist attacks, several boys attacked Shirin and choked her with her scarf. Because of the racism and prejudice Shirin has experienced throughout her life, she has developed a thick skin. At school, she talks to no one, looks at no one, and does her best to stay under the radar. She has a quick temper, however, and automatically assumes that anyone looking at her or talking to her has malicious or racist intent. Navid, who is far more outgoing than Shirin, starts a breakdancing team with his friends Jacobi, Carlos, and Bijan. He then invites Shirin to join them, which she does. They get a teacher to sponsor the activity, which means they get a room to practice in after school.

Shirin meets a boy named Ocean when they are partnered in biology class to dissect a cat. Because they still have to write a report, she gives him her phone number, and their friendship begins even if it gets off to a rocky start. As they get to know each other, Ocean expresses interest in Shirin’s family and her culture, and they begin texting and talking on the phone. Ocean and Shirin are also both in a class called Global Perspectives, which is taught by Mr. Jordan. When Mr. Jordan uses Shirin to illustrate a point about prejudice, Shirin gets upset and leaves class. Concerned, Ocean follows her, and the two sit at an IHOP and talk, feeling a mutual attraction. 

At lunch one day, Shirin meets a boy named Yusef, another Muslim, who is a senior. At practice, Jacobi tells Shirin that her constant anger is not healthy, which makes her question her defensiveness. Shirin attempts to drop Mr. Jordan’s class, but then he apologizes to her and asks her to return to class, which she does. Ocean tries to get to know her more, and one day they collide in the hallway and accidentally embrace. The physical contact exhilarates them both, and they soon admit their strong feelings for each other. Shirin believes that their relationship will not be good for either of them because of their fellow students’ bigotry. She tries to avoid Ocean, but she finds that she cannot. One day, they kiss in Ocean’s car during lunch, and other students see them. Word spreads quickly that they are a couple.

Shirin discovers that Ocean is a junior and a star basketball player on whom the school and varsity team depend to win championships. She realizes she had no idea what a big deal he was. Ocean confides in Shirin, telling her he doesn’t like playing basketball but doesn’t want to let down his mother, Coach Hart, the team, or the school. Ocean tells Shirin about his parents’ divorce and his mother’s inheritance. Ramadan arrives, and Shirin’s family begins their fasting, which Shirin likes but Navid hates. Shirin invites Ocean to attend a breakdancing event with her one Saturday night, and Navid gives them one hour alone afterward. During their time alone, Ocean takes Shirin to the park where he learned to play basketball. When Shirin expresses her concern for his unhappiness, Ocean feels moved by her compassion for him.

Ocean attends Thanksgiving dinner at Shirin’s house and falls in love with her family and the food. In her room, they kiss again, until Navid cuts their time alone short when he knocks on the door. Later, on the phone, Ocean admits that he is falling in love. As he and Shirin are both tired of hiding their relationship, Shirin agrees to let Ocean drive her to school. In the parking lot, someone calls her “Aladdin,” and someone else throws a cinnamon roll at her, which gets frosting all over her face and scarf. When she goes to the bathroom to wash up, a girl snaps a photo of her without her hijab on and posts it online for the entire school to see. 

Later, Navid and the other breakdancers attack the person who threw the roll. Someone posts a letter accusing Ocean of being a terrorist sympathizer because Shirin is his girlfriend. Coach Hart tells Ocean to stay away from Shirin, but Ocean refuses. Coach Hart then screams at Shirin for ruining Ocean’s life and jeopardizing his scholarship. Even Ocean’s mother, Linda, approaches Shirin and tries to talk her into breaking up with Ocean. Linda admits that she has spent Ocean’s college money, so he needs a basketball scholarship to continue his education. Ocean begs Shirin not to break up with him, but she wants to protect him, so she begins avoiding him completely. Ocean is heartbroken. After he sees her with Yusef, who has joined their breakdancing team, Ocean is suspended for fighting.

After Navid’s breakdancing team wins the school talent show, students begin to change their attitudes toward Shirin, and their hypocrisy angers her. One day, Ocean approaches her locker, and they share how much they miss each other. When Shirin returns to her locker after breakdancing practice, she realizes she never locked it. While nothing has been stolen, she notes that her journal has been moved from the bottom to the top, and she suspects Ocean read it. She feels upset by this idea but also grateful that he might now know her deep, true feelings for him. After Ocean gets suspended again—this time for breaking Coach Hart’s nose, he appears at Shirin’s house one morning, and they skip school together. 

Back at Ocean’s house, Ocean apologizes for reading Shirin’s journal, and they kiss again. When they embrace, Shirin notes that it feels like they have been drowning in a very large expanse of sea. Ocean’s mother hires a lawyer for his hearing. After the hearing, Ocean avoids getting expelled from school, but he quits the basketball team. Shirin and Ocean spend the last few months of the school year together and happy, but at the end of the year, Shirin’s family moves again. Ocean stands in the street and watches Shirin and her family drive away. When he is no longer in sight and just when Shirin feels her heart will break, Ocean texts her, “Don’t give up on me.” The story ends with Shirin stating, “And I never did.”