After glimpsing an older man in a room with a dead girl, sixteen-year-old Allie, who has a life-threatening allergy to sunlight, discovers she is the lone key to stopping a serial killer.
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 from 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—and the murderer sees them, too. A game of cat-and-mouse ensues that escalates through the underground world of experimental treatment, off-the-grid sports, and forbidden love. Allie, who can never see the light of day, discovers she alone can stop a human monster.