An inventive fantasy adventure rooted in Arthurian legend but set in the present--where a secret Eighth Day exists. When Jax Aubrey wakes up the morning after his 13th birthday to a world with no people, he does what anyone would do: assumes it's the apocalypse, stocks up on survival supplies, and fortifies his house against zombies. When he wakes up the next morning to a normal Thursday, Jax wonders if he's lost his mind. But his 18 year-old guardian, Riley Pendare, explains that there is an extra day squeezed between Wednesday and Thursday. Some people, like Jax and Riley, are Transitioners, and live in all eight days. Others, including Evangeline, the teenage girl who's been hiding out in the house next door, exist only on this special day. Jax is intrigued by Evangeline, who should be more than 100 years old, but because she lives only one day a week, is still a teenager. When Jax attempts to befriend her, he learns that she is the key to a spell cast during King Arthur's reign.

Riley is her reluctant jailor, sworn to keep her safe from enemies who would use her to eliminate the other seven days of the week, leaving only those with access to the Eighth Day alive. They'll kill her if they can't get what they want. So when Jax accidentally leads a pack of human bloodhounds to her door, he's confronted with a terrible choice: face a real apocalypse or sacrifice Evangeline.