Special agents, a secret bunker, and ancient magic that nobody was prepared for....

Recovering from injuries, Mattie is chomping at the bit to go and rescue her sister, Tillie, and her friend, Trevor. Especially after a new ally reveals that they're most likely being held in the same super secret underground headquarters where the leader of the entire organization is holing up.

Meanwhile, inside the bunker, Tillie and Trevor are trapped in cells with no doors or windows, and their mage powers aren't working. Escape seems impossible, but then again . . . impossible has never stopped them before.

Will Mattie, Tillie, Trevor, and their friends be able to defeat the Auditors once and for all, or will they be crushed under the relentless heels of an ancient power? Find out in the final installment of the Mathilda Holiday series.