Stella Grant is a senior in high school and a cystic fibrosis patient at Saint Grace’s Hospital. She’s been going to the hospital regularly since she was six years old for checkups and treatments. Now, she is beginning a one-month stay at Saint Grace’s due to a flare-up of her illness. Stella is scared because her lungs are weaker than ever before. She tries hard to stay healthy, because she worries that her parents wouldn’t be able to cope if she dies. Stella is on a waiting list for a lung transplant.
On her first day back at the hospital, Stella learns that there is a new cystic fibrosis patient at Saint Grace’s, Will. When Stella first meets Will she thinks he is attractive but very arrogant. Will finds Stella attractive too. He finds her popular YouTube channel where Stella has hundreds of videos about cystic fibrosis. Stella learns that Will has B. cepacia, an infectious disease that is deadly for people with cystic fibrosis. All cystic fibrosis patients must stay six feet apart from each other because of the risk of cross infection, but it’s especially important for Will due to the risk of infecting others with B. cepacia. Will is not eligible for a lung transplant because of it. He likely has only a few years to live, but he is at Saint Grace’s for an experimental drug trial.
A couple days after they meet, Stella goes to Will’s room to look at his treatment plan. Will is careless about his treatments, because he thinks they stop him from experiencing life. Stella is worried for his health, so she makes a deal with him—they will do all their treatments together over video calls so that Stella can make sure Will is doing them, and in exchange Will can draw Stella’s portrait. He loves to draw and is a talented artist. Will and Stella spend much of their time on video calls with each other over the next few days and find that they greatly enjoy each other’s company.
One day, Will asks Stella about a drawing in her room that Stella’s sister Abby did. Will realizes that Stella never talks about Abby, and he suspects that Abby passed away. He goes to meet Stella and, somewhat tactlessly, asks if Abby is dead. Stella is angry at his callousness and cries, but she explains that her sister’s death is the reason that she takes her treatments so seriously—she feels that she must stay alive for her parent’s sake. Will tries to argue that living such a strictly limited life isn’t worth it, but this enrages Stella even more. Later when she is alone in her room, Stella reminisces about Abby, who died in a cliff diving accident a year prior. Stella was supposed to be on the trip too but ended up staying home, so she feels somewhat responsible for Abby’s death. That evening, Will apologizes to Stella, and she forgives him. Stella is scared because the next day she will undergo surgery for an infection in her skin, even though anesthesia is risky since her lungs are so weak. Will realizes that it will be her first surgery without Abby.
Will sneaks into the operating room before Stella’s surgery and sings a song Abby used to sing to Stella before major procedures. Stella is terrified for her surgery, but Will makes her feel better. She feels that she’s in love with him. When Will leaves, Stella’s favorite nurse, Barb, catches him and reprimands him for going to the operating room. She tells Will that she once had two patients who were in love, and they both ended up dying because they didn’t stay six feet apart—one of them gave B. cepacia to the other.
After her surgery, Stella texts Will to meet her, but he doesn’t come. Poe, Stella’s best friend at the hospital, tells Stella that he overheard Barb’s conversation with Will, and that Will doesn’t want to see Stella. Stella is devastated. She and Will both spend the next few days feeling lonely and wishing they could be together, but Will doesn’t want to risk endangering Stella. A few days later, Stella sends Will her newest YouTube video. In it, she says that she is going to reclaim one foot of distance, and only stay five feet away from Will instead of six. Stella explains that cystic fibrosis has stolen much of her life, so she deserves to take back one foot of distance. Stella goes to Will’s room, using a pool cue to measure five feet between them, and Will happily agrees that they will continue to spend time together. They go on a date around the hospital that lasts hours. Will feels like he’s falling in love with Stella. On the date, they look out at a cluster of holiday lights in a nearby park. Stella says that she and Abby used to visit the lights together every winter, and Abby would make a wish for Stella to get new lungs.
The next day is Will’s 18th birthday. He was looking forward to becoming a legal adult so that he could choose to leave the drug trials his mother has put him through for years, but now Will wants to try to live longer. Stella sets up a surprise party and dinner for Will. At the party, Poe tells Stella that he is getting back together with his ex-boyfriend Michael, and Stella is thrilled for him. That night, Stella wakes up to an alarm blaring and hospital staff rushing into Poe’s room—his heart stopped. Stella and Will wait while doctors try to resuscitate Poe, but they are unsuccessful, and Poe dies.
The next night, Will and Stella embark on a two mile walk through the snow to see the holiday lights. They stop to slide around and dance on a frozen-over pond. Stella gets an urgent text from Barb that the hospital received lungs for her. Stella has to go into surgery in a few hours, but Stella decides to stay with Will instead. Suddenly, Stella slips and falls, breaking the ice over the pond, and she falls through into the water. Will calls the hospital, pulls Stella out, and gives her CPR when he sees that she’s not breathing. Administering CPR is very taxing because Will’s lungs are also weak, and he faints. They both wake up at the hospital. Stella doesn’t want to do the lung transplant, because it would make her situation with Will worse—cross-infection would become an even greater risk—but Will convinces her to do the transplant. Stella’s surgery is successful, and she doesn’t contract B. cepacia even though Will gave her CPR. Meanwhile, Will’s drug trial is not effective. Before leaving, Will says an emotional goodbye to Stella over the phone from the hospital’s courtyard. They can see each other through the window. Will has somehow lit up the courtyard with the holiday lights from the park.
Eight months later, Stella has healed from her surgery and is in good health. She’s at the airport with her friends—they’re about to fly to Rome. She sees Will, who is about to board a flight to Brazil. He looks very sick. They lock eyes and walk towards each other until they’re five feet apart.