Jax Aubrey, an ordinary twelve-year-old, discovers his guardian Riley is part of a secret race of people called the Kin, who live in an eighth day of the week invisible to regular people. When Jax accidentally binds himself to a powerful Kin girl named Evangeline, he is thrust into a centuries-old war between the Kin and a ruthless group called the Transitioners who want to destroy the eighth day. Jax must learn to control his own emerging magical talents and navigate this hidden world to protect those he loves and prevent a catastrophe that could unravel time itself.