When Jax wakes up to a world without any people in it, he assumes it's the zombie apocalypse. But when he runs into his eighteen-year-old guardian, Riley Pendare, he learns that he's really in the eighth day—an extra day sandwiched between Wednesday and Thursday. Some people—like Jax and Riley—are Transitioners, able to live in all eight days, while others, including Evangeline, the elusive teenage girl who's been hiding in the house next door, exist only on this special day. And there's a reason Evangeline's hiding. She is a descendant of the powerful wizard Merlin, and there is a group of people who wish to use her in order to destroy the normal seven-day world and all who live in it. Torn between protecting his new friend and saving the entire human race from complete destruction, Jax is faced with an impossible choice. Even with an eighth day, time is running out.