Everything, Everything centers on Maddy, a girl allergic to the outside world, who hasn't left her house in seventeen years. The only people she interacts with are her mother and her nurse, Carla. When a new boy named Olly moves in next door, Maddy is drawn to him despite the inherent risks due to her condition. The story unfolds with her navigating feelings of love and the dangers of her illness, told through a blend of vignettes, diary entries, and illustrations.