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.