Hidden within the old stone walls of Saint Bartholomew's Church lives a lively, resilient colony of mice. They are happily out of sight from the humans, but their peaceful existence is constantly under threat. While the mice certainly fear the stray cats that roam the grounds, they are absolutely terrified of the Great X the dreaded exterminator. When signs of the Great X begin to appear, the colony looks to their brave and clever leader, Mouse Mistress Hildegarde. Hildegarde knows that keeping her flock safe will require brilliant planning and incredible teamwork. Alongside her loyal friend Roderick, she must guide her fellow mice through a series of wild, heart-pounding dangers, escaping traps sometimes by just the skin of their tails. Their ultimate goal is to hold out until the highly anticipated feast day of Saint Francis, the patron saint of animals. If they can just survive long enough to receive Father Murphy's blessing, they might secure their safety forever. This charming, funny, and deeply adventurous tale proves that even the smallest creatures can possess the bravest hearts.