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.

Allie Kim’s fatal allergy to sunlight, XP, still confines her to the night. Now that she’s lost her best friend Juliet to an apparent suicide, the night has never felt darker—even with Rob at her side. Allie knows why Juliet killed herself: to escape the clutches of Garrett Tabor, whom the trio saw committing an unspeakable crime. Garrett is untouchable; The Tabors founded the world-famous XP clinic that keeps Allie and Rob alive and their small Minnesota town on the map. Allie can’t rest until Garrett is brought to justice. But her obsession jeopardizes everything she holds dear. Not even Parkour can distract her; nothing reminds her more that Juliet is gone. When Rob introduces Allie to the wildly dangerous sport of nighttime deep diving, Allie assumes he’s only trying to derail her investigation... until they uncover the horror terrible secret Garrett Tabor has hidden under Lake Superior.