Vivien, Bella Thorne, is a bright high school student who loves math and physics, navigating a world where privilege and popularity shape choices and futures. Steve, Sebastiano Pigazzi, is the clean-cut star of the swim team and Vivien's boyfriend, yet he often vanishes without explanation, leaving her to wonder if she can trust him. Roy, Benjamin Mascolo stands in sharp contrast—poor, tattooed, and underperforming on the same team—under pressure from both the coach and his father to improve, because a Rome meet in two weeks could unlock a college scholarship.
Vivien's suspicions about her mother's fidelity come into focus when she tails her to a restaurant far from home and witnesses an indiscreet affair with a man who isn't her husband. Upset, Vivien is harassed by a group of teens, and Roy, who knows them, steps in to help. He suggests Vivien steer clear of that side of town, having recognized his teammate's girlfriend.
Steve has been distant and inattentive, disappearing and never calling when she needs him, leaving Vivien unsure of her own knowledge. She does go to the venue, but postpones taking her quantum physics test. In the background, Steve's secrecy deepens as he maintains a hush-hush relationship with Dylan, the college-aged swim coach—Dylan, Nikolay Moss, has been seen with Steve in moments that raise the stakes for everyone involved.
At a costume party with her best friend, Vivien crosses paths with Roy on the dance floor. A fistfight erupts as Roy defends a longtime friend—the tattoo artist who started inking him at 13—adding another layer of tension to the already complicated web of loyalties. Later, Steve and Roy duel in the pool, and Roy defeats Steve to earn a place on the Rome-bound team. A tense confrontation follows between Vivien and Steve; she gives him an ultimatum about their relationship, and he leaves with the rest of the team.
Back home, Vivien learns that her parents separated a year earlier but had been waiting to tell her until college. Distraught, she travels to Rome to surprise Steve, but ends up spending the day with Roy instead. They wander the city, take a rowboat ride, and drink at a hotel bar, running out on the bill. The day culminates in a kiss in a pool, leaving Vivien with mixed feelings as she returns to Steve's hotel room only to find him in bed with the coach.
Shocked and heartbroken, Vivien runs from the hotel with Roy in pursuit. In a dark street, she lashes out with hurtful words before Roy chases after her to apologize. That night, Vivien is hit by a car and rushed to a Rome hospital, where doctors work to stabilize her. She regains consciousness days later and, at first, cannot remember what happened; Steve lies about the day, and Roy keeps his distance. A song the two heard in Rome and photos from their day gradually jog Vivien's memory, and she starts to piece together the truth.
With memories returning, Vivien seeks out Roy, and they spend the night together. Reconnected and newly confident in herself, she faces her quantum physics test with a clearer sense of who she is and what she wants to pursue. The experience leaves her ready to chart her own path, informed by the day that forever altered her relationships and her self-belief.
