Olly moves in next door to Madeline and they begin to online message. Olly comes over to Madeline's house for the first time, without Madeline's mom knowing.
Madeline and Olly develop feelings for each other. Despite Madeline's condition, she convinces Olly to go to Hawaii with her. While in Hawaii, Madeline gets sick and ends up in the hospital. They eventually come home and do not talk to each other due to close supervision by Madeline's mom. Olly and his family eventually move away.
Madeline receives an email from the hospital she was in suggesting she may not have SCID. After questioning her mom, she is convinced it was just a mistake. After further investigation, it becomes evident that she does not have SCID after all and it was just her mom attempting to protect her after the grieving loss of her husband and son.
Madeline does not talk to her mom and she begins to go outside periodically to build up her immune system.
Madeline leaves her mom and goes to New York to find Olly. She texts him to meet her at a book store and they reunite.