Allie Kim suffers from Xeroderma Pigmentosum: a fatal allergy to sunlight that confines her and her two best friends, Rob and Juliet, to the night. When freewheeling Juliet takes up Parkour—the stunt-sport of scaling and leaping off tall buildings—Allie and Rob have no choice but to join her, if only to protect her. Though potentially deadly, Parkour after dark makes Allie feel truly alive, and for the first time equal to the “daytimers.”

On a random summer night, the trio catches a glimpse of what appears to be murder. Allie alone takes it upon herself to investigate, and the truth comes at an unthinkable price. Navigating the shadowy world of specialized XP care, extreme sports, and forbidden love, Allie ultimately uncovers a secret that upends everything she believes about the people she trusts the most.