After solving the mystery of Tilly's mother's disappearance, Tilly and her best friend Oskar, discover that the bookwandering community is at risk. Tilly and Oskar are part of a special group of people, bookwanderers, that can travel inside any book they want to. But one day in Paris, France, the friends stumble into a book of fairy tales where strange things are happening. Plus, an extreme group of librarians have taken over the British Underlibrary and are determined to stop bookwandering. Tilly and Oskar believe The Archivists are the key to setting things right, but they haven't been seen for thousands of years and some people don't even believe they ever existed. On their quest for The Archivists, the two friends realize that villains don't only live inside books and sometimes there is no happily ever after.
