Skye Aitken is an adolescent girl who is told she has reached the final stages of her cancer and has little time left. Her prognosis casts a heavy shadow over her days, pushing her to decide what matters most and to seek meaning in small, urgent moments. She approaches life with a blend of blunt honesty and fierce curiosity, determined to leave a mark on the world while she can still feel the sun on her face.
Calvin Lewis is a young man working as a baggage handler at the airport, alongside his father and elder brother Frank. He harbors a quiet crush on Izzy, a flight attendant, but his fear of talking to her—and of dying—keeps him at a cautious distance from romance. His doctor worries that his worry could be a hypochondria, and encourages him to join a cancer support group to gain perspective beyond his own fears.
At the support meeting, Calvin encounters Skye, and she immediately shows an interest in him. Although he insists that he does not have cancer, they quickly become friends, and Calvin offers to help Skye complete her list of things to do before she dies. Initially, her blunt, unpredictable manner unsettles him, yet he grows to value her company and finds it hard to imagine life without their conversations.
Skye goes to a high school party with Calvin, where she witnesses a friend kiss Will, the boy she has a crush on. As Calvin and Skye begin spending more time together, Calvin slowly begins to overcome his fear of dying.
Skye uses her matchmaking energy to set up a date for Calvin with Izzy, during which she falsely informs Izzy that Calvin also has cancer. Izzy grows more interested in him, and the two begin dating. Skye later reveals to Calvin that she has always known he does not have cancer, though Calvin hesitates to tell Izzy the truth, worried that she might like him only because she thinks he’s sick.
Skye learns from Lucy, Calvin’s sister-in-law, that his mother “shut down” after the death of his twin sister in a car accident when they were eight. Calvin finally admits to Izzy on a date that he doesn’t have cancer, but she breaks up with him because she is hurt by the lie.
Skye decides to lose her virginity to Will, a choice that adds a new layer to her sense of agency and the complexity of her relationships.
Calvin becomes depressed after the breakup and stops going to work, but his father pushes him to return to his duties. Meanwhile, Skye confesses to Calvin that she was disappointed after losing her virginity to Will because it happened so quickly.
After Skye passes out in public and is rushed to the hospital, Lucy goes into labor, allowing Calvin and Skye to meet his new niece. Frank and Lucy announce that they want Skye and Calvin to be the baby’s godparents, even as Skye points out that she does not have long to live. Calvin experiences a panic attack, but Frank helps him calm down and reminds him that Skye still needs him.
Calvin makes efforts to help Skye finish the rest of the items on her lists with a little help from Izzy and Skye’s parents. He also opens up about why he stopped celebrating birthdays, a memory tied to his mother after his twin sister’s death. After Skye passes away, Calvin receives birthday cards in the mail from her to make up for the ones he didn’t celebrate. He finally finds the courage to face his fear of heights and decides to take a trip on a plane. During take-off, Izzy and Calvin exchange a knowing look, suggesting that they may be headed toward a reconciliation.
