Maddy is 17 and lives in a room that’s entirely white. She loves to read, but all of her books come to her decontaminated. In every book, she writes her name and fantastical rewards for anyone who might find one, despite the fact that nobody will ever find a lost book of hers. Maddy has SCID, an autoimmune disease that renders her unable to leave the house, since doing so would mean risking death. She lives with her mom, Dr. Whittier, and her nurse, Carla, is the only other person Maddy sees regularly. On Maddy’s 18th birthday, Mom and Maddy make Maddy’s traditional birthday cake—a white cake with vanilla frosting—and they play games. This birthday is especially hard: since although Maddy is now a legal adult, because of SCID nothing about her life is going to change.
A few days later, Maddy hears a rumble and beeping outside. Carla is concerned, but Maddy rushes to the window. She sees a family with two kids about her age moving in next door. The boy wears all black and is extremely handsome. Over the next week, Maddy learns the family’s schedule. The boy, Olly, is unpredictable, while his sister, Kara, smokes and spends time on her phone. Olly’s mom gardens while Olly’s dad goes to work. When the father gets home in the evenings, he yells for hours. During one of Mom and Maddy’s Friday night dinners, Olly and Kara knock on the door with a Bundt cake from their mom. Mom refuses the cake and when Olly’s dad learns about this, he throws the cake at Olly. Olly’s window is right across from Maddy’s, but he refuses to look at her that night. Because of her interest in Olly, Maddy finds it hard to be happy with just her books, especially when, a few nights later, Olly stages a weeklong drama on his windowsill in which the Bundt cake—which is, according to Olly, indestructible—attempts to commit suicide and dies in the hospital. After this, he and Maddy exchange email addresses and begin to talk online. Maddy admits that she’s too ill to leave the house. Olly is both cynical and charming, and he admits that his dad hits his mom regularly.
Maddy prepares for a rare in-person critique with her architecture tutor, Mr. Waterman. He arrives, studies her model buildings with delight, and finds the astronaut that she always hides in each model she builds. This time, astronaut in an ice cream shop surrounded by food, but Mr. Waterman notes that the astronaut won’t be able to eat any of it with his helmet on. Later, Carla realizes that Maddy has been talking to Olly and after two days, agrees to let him visit in the sunroom as long as Maddy doesn’t touch him. During their visit, Olly tells Maddy what it’s like to swim in the ocean. The next morning, Maddy is convinced she’s sick, but Carla declares that she’s just lovesick. Terrified of her desire for more, Maddy asks Olly not to email her over the weekend—but on Monday when she finds no emails waiting for her, she’s distraught. Carla encourages Maddy to understand that love won’t kill her, so Maddy resumes communication with Olly on the understanding that they’ll just be friends.
Carla allows Olly to visit again a week later. Maddy deliberates over what to wear and decides that it’s time to change up her closet of white tee shirts, Keds, and blue jeans for more colors. She tells herself that it’s okay to lie to Mom about this. Olly suggests that in theory, it’s possible to find and change one moment that would fix everything and make things better. Maddy knows she’s falling in love with him and begins to cancel movie nights with Mom so she can chat with Olly. She realizes that she and Mom are growing apart because Maddy has a secret. Maddy witnesses a night of violence at Olly’s house, and when he visits the next day, she feels the urge to touch Olly and comfort him. Olly explains that his dad only became violent about a decade ago, after he was fired from his job. Young Olly was too afraid to comfort his dad and a few months later, when Olly’s dad hit his mom for the first time, Olly wondered if comforting him would’ve changed things.
A few days later, Carla threatens to not let Olly visit if Mom continues to notice changes in Maddy. She points out that Olly will go back to school soon and get a girlfriend, and that Mom is lonely and distraught. Despite Carla’s warning, Maddy just wants to be able to have secrets, so she applies for a credit card. When Olly visits next, he teaches Maddy to do a handstand. When she wobbles, he grabs her ankles and when she’s standing on her feet again, they hold hands. On instant messenger later, Olly suggests that they could kiss. During Olly’s next visit, they do just that. Maddy feels her world change instantly. Several days later, as Maddy plays a game with Mom, they hear screaming outside. From the window, Maddy and Mom see Olly’s dad swing at Olly and Olly’s mom. When Olly’s dad manages to punch Olly in the stomach, Maddy races outside without thinking and screams at him to stop. Realizing that Maddy has been seeing Olly, Mom is distraught and takes action: she fires Carla and takes away Maddy’s internet privileges. Olly and Maddy take to miming and writing on Olly’s window to communicate.
Mom hires a new nurse named Nurse Janet, who annoys Maddy to no end. Olly messages Maddy when he can during school and Maddy remains morose and upset. When Mom visits Maddy one night, she offers her a framed photograph of herself, Maddy, Maddy’s dad, and Maddy’s brother on vacation in Hawaii, one month before Maddy’s dad and brother died in an accident and two months before Maddy’s SCID diagnosis. Maddy begins to realize that the “experiences” she has in books are no substitute for experiencing things firsthand. Her life doesn’t make sense anymore, and strangely, she finds that she’s willing to die if it means she gets to live. She writes Mom a goodbye letter and sneaks out in the middle of the night. She lies to Olly that she purchased pills from Canada that will delay her symptoms and asks him to go to Hawaii with her. He doesn’t really believe she has pills, but he agrees to go. Before they go to the airport, they stop to visit Carla. Carla seems aware that Maddy is lying about the pills, but tells Maddy about her experience leaving Mexico. It gave her freedom, but she regrets leaving for various reasons—and she suggests to Maddy that experiencing regret is a part of living.
Maddy and Olly land in Hawaii. At the baggage carousel, Olly proposes that baggage carousels are a perfect metaphor for life and that people are the suitcases. He suggests that his dad is the carousel, but when Maddy takes offense to this, he sweet-talks a greeter into giving Maddy a lei. They get a taxi to their hotel and the driver agrees to stop so that Maddy can wade into the ocean. At the hotel, the receptionist welcomes them to Hawaii for their “honeymoon” and shows them to their room. They awkwardly note that there’s only one bed as Olly flips through The Little Prince, which Maddy brought because it’s her favorite book. Suddenly, Maddy experiences vertigo and chest pain. She realizes she’s hungry.
After they eat, Maddy and Olly buy souvenirs and beach gear. Maddy chooses to send Mom a postcard, feeling weird about making memories without Mom for the first time ever. Maddy and Olly snorkel and dive off cliffs, which surprisingly doesn’t scare Maddy. In the afternoon, they meet up with Zach, a friend of Olly’s. He’s gay and wants to be a rock star, but he hasn’t told his parents either of these things in order to keep the peace. Olly receives emails from Maddy’s mom saying that she’s on her way and asks Maddy to deal with them. Maddy is angry and asks Mom not to come. When Olly goes to the bathroom, Zach ascertains that Maddy lied about the pills. He suggests that part of growing up is disappointing the people they love. Back at the hotel, Maddy and Olly regard the single bed again and Olly admits that he’s nervous. They lie down, say they love each other, and eventually decide to have sex. The experience makes Maddy feel like she knows all the secrets of the universe, and she feels very close to Olly. After dark, they eat and then sit on the beach. They discuss Olly’s dad’s violence and Maddy tells Olly he needs to escape his household for his own safety.
Maddy wakes up in the middle of the night, seriously ill. Her heart stops in the ambulance. Mom arrives and against Dr. Francis’s advice, insists on taking Maddy home. Maddy takes a few weeks to recover and decides that love is awful—she wants nothing to do with it. She breaks things off with Olly, knowing that she can’t go back to non-touching visits when she now knows what the world is like. She deletes all of his emails and spends lots of unhappy time with Mom, who allows Carla to return to work. A month after the trip, Maddy sees Olly, his mom, and Kara frantically moving out during the day. Around Christmas, Olly’s dad moves too. Maddy goes through all the deleted emails from Olly. He thinks that his mom may have decided to leave when Olly told her about Maddy and tells her how brave she is for wanting to live, even if it might kill her.
Not long after, Maddy receives an email from Dr. Francis. Dr. Francis writes that she doesn’t think Maddy has SCID, includes test results, and suggests that Maddy get a second opinion. Maddy researches by herself and takes the printed email to Mom. Mom reacts strangely and says disturbingly that she had to protect Maddy. The next day, Maddy shows the email to Carla. Carla’s reaction is even more disturbing: she thinks that Mom might not have recovered after losing her husband and son, and she’s suspected at points that Mom is unwell. That night, Maddy goes through Mom’s office looking for her SCID diagnosis. She finds nothing but proof that she was a sickly baby and annotated articles on SCID off of the internet. When Mom arrives and accuses Maddy of taking the diagnosis papers, Maddy vomits outside and screams at Mom.
Four days later, Maddy meets with a SCID specialist named Dr. Chase. He confirms that Maddy doesn’t have SCID, but says that Maddy’s immune system is fragile nonetheless—growing up in a sanitary environment means that Maddy’s immune system has no practice fighting off common bacterial and viral infections. Maddy yearns for answers, considers emailing Olly, and installs a lock on her door. She paints her walls different colors, opens the windows, and purchases goldfish. Mom begins to seek counseling and Carla gently tells Maddy that she needs to find another job since Maddy doesn’t need her anymore. Though Maddy is angry with Mom, she accepts Mom’s gift of a cellphone and purchases tickets to New York City. As she leaves, she tells Mom that she’s not sure their house is her home anymore. Maddy arranges a surprise for Olly in a used bookstore. There, he discovers her copy of The Little Prince and reads that the reward for finding it is Maddy herself. Maddy steps out from behind a shelf.
