“A” is a traveling spirit who experiences every day in the body of a different teenager. A wakes up in the body of Justin, the neglectful boyfriend of Rhiannon. At school, Rhiannon approaches A as Justin, convincing A to skip school with her. As the day goes on, A falls in love with Rhiannon, as she confides her troubled home life following her father’s mental breakdown, almost resulting in her family losing their home. Rhiannon feels a rekindled love for Justin, seemingly a more thoughtful and caring person. The next day, Rhiannon finds Justin has reverted to his old, careless self and does not remember the previous day. Meanwhile, A wakes up in the body of Amy and masquerades as an exchange student to be close to Rhiannon.
Waking up as Nathan, A attends a party and finds Rhiannon. Dancing together, A and Rhiannon bond, and A tells Rhiannon she deserves better than Justin before Justin chases A off. A few days later, A texts Rhiannon to meet, and she does, assuming she is meeting Nathan. A arrives as Megan, explaining that A was Justin, Amy, and Nathan, and has fallen in love with her. Initially disdainful, Rhiannon agrees to meet with A the next day. Now in the body of James, A reveals that A has shifted bodies every day since infancy and shares the private Instagram account with pictures taken in every body, through which Rhiannon can communicate with A. Meeting with Nathan, who believes he was possessed by the devil, Rhiannon realizes A is real. A, in the body of transgender teen Vic, convinces Rhiannon to give A a chance, suggesting that it is the soul that matters, not the body. After some thought, Rhiannon agrees to continue meeting A.
Surprised to awaken in the body of Rhiannon herself, A sees it as an opportunity to get to know Rhiannon better. A promises to be respectful of Rhiannon’s privacy and her life, not breaking up with Justin or looking at Rhiannon’s naked body. Over the course of the day, A bonds with Rhiannon’s mother, as well as her sister and father. The following day, having finally found the courage, Rhiannon breaks up with Justin. She immediately calls A for a weekend trip at her uncle’s cabin. A, in the body of Xavier, talks about the day spent in Rhiannon’s body. Rhiannon tells A that leaving a mark could be a wonderful thing so people will know A exists, but A feels obligated to leave people’s memories unchanged. At the end of the day, A kisses Rhiannon goodbye and promises to return the next day but does not, forcing Rhiannon to call her mother to pick her up. A later explains that day’s body was undergoing a lung transplant. Rhiannon and A gradually become intimate and promise they will figure out how to maintain their relationship.
A wakes in the body of the suicidal Kelsea, and Rhiannon convinces A to attempt to hold onto Kelsea’s body for more than twenty-four hours, to keep her alive until Kelsea’s father can be alerted to her struggles. A is successful, and Rhiannon convinces A to stay in the body of her classmate, Alexander, so they can remain together. Though this seems to work for a short time, A is unwilling to take over somebody else’s life permanently. Inviting Rhiannon to Alexander’s house, A declares that they cannot realistically be together forever, and that Alexander himself is perfect for Rhiannon. Sharing one last night together, Rhiannon and A kiss goodbye, and wait for A to fall asleep. The next day, A awakens in another body and drives to New York while Rhiannon meets Alexander at school.