In a small hospital town, a trio of teens rebel against their fatal diagnosis of XP (an allergy to sunlight) with late night Parkour, an extreme sport of daredevil risks. On a random summer night, while scaling a building like any other, the three happen to peer into an empty apartment and glimpse an older man with what looks like a dead girl. A game of cat-and-mouse ensues that escalates through the underground world of hospital confinement, off-the-grid sports, and forbidden love. Allie, who can never see the light of day, discovers she's the lone key to stopping a human monster.