Lilly is a sunwalker-a vampire born from human parents, able to walk in the daylight. She lives life as human, hiding her true identity from all those around her. One evening, she comes to the rescue of her best friend, Lex, as a vampire is about to make a meal out of her. Lilly is drawn to him, despite her desire to loathe him for almost murdering Lex, as he is the first of her kind she has ever met. As the vampire, Tread, begins to open Lilly's eyes to a world she has never known, Lilly must decide where she belongs. After she is betrayed by the person she loves most, Lilly is forced to submerge herself entirely in the vampire world, only to discover that Tread has a secret so shocking it could destroy them all.