For millennia, the Librarians have secretly protected the world by keeping watch over dangerous magical relics. Cataloging and safeguarding everything from Excalibur to Pandora's Box, they stand between humanity and those who would use the relics for evil.

Stories can be powerful. In 1719, Elizabeth Goose published a collection of rhyming spells as a children's book, creating a spellbook of terrifying power. The Librarian of that age managed to dispose of all copies of the book except one, which remained in the possession of Elizabeth Goose and her family, temporarily averting any potential disaster.

However, strange things are happening. A window washer in San Diego who was blown off his elevated perch by a freak gust of wind, but miraculously survived by landing on a canopy over the building entrance. A woman in rural Pennsylvania who was attacked by mutant rodents without any eyes. And, a college professor in England who somehow found herself trapped inside a prize pumpkin at a local farmer's market. Baird and her team of Librarians suspect that the magic of Mother Goose is again loose in the world, and with Fynn Carson AWOL once again, it is up to Cassandra, Ezekiel, and Stone to track down the missing spellbook before the true power of the rhymes can be unleashed.