Maddy, an 18-year-old girl, lives in complete isolation within her home due to a severe immunodeficiency that makes her allergic to almost everything. Raised by her protective mother, Pauline, Maddy's life is regimented and sterile, involving daily routines that keep her safe from potential infections. Her only in-person contact is with her nurse, Carla. However, Maddy's monotonous existence changes dramatically when a new family moves in next door, including a teenage boy named Olly. Through their bedroom windows, they exchange glances and eventually start texting, leading to a growing friendship and deeper emotional connection.

As Maddy and Olly's bond strengthens, her yearning to explore the world beyond her home intensifies. Despite the risks, she decides to take bold steps to experience life and love firsthand. Her actions bring unforeseen challenges and revelations that profoundly impact both her and Olly's lives. The story follows Maddy's journey of breaking free from the constraints imposed by her illness and discovering the breadth of human experience and emotion.