Seven heroic mice join the Mouse Guard.
Francisca, Marx, and Tander are sent out to protect a caravan of grain, on its way to found the new city of Wildseed. After securing the caravan, they head to Port Sumac to acquire new maps for the territories, then proceed to Calagaro Outpost to defend it from migrating crabs.
Lily, Sable, Isolde, and Zeke are sent out to mark the scent border that protects the Territories. Along the way, snakes, bureaucracy, supply problems, and theft stall their efforts.
Lily, Sable, Isolde, and Zeke are given a mail route and find an adventure in every town they enter. Their relationships are tested by secrets; some of which they bring with them.
Marx, Francisca, and Tander escort a large group of settlers to new homes in Wildseed. Through the dangers they face, they see a community be born.
Francisca, Tander, Zeke, and Isolde ride out to protect an outpost from the largest creature they've ever seen, and they find a mystery they are compelled to follow.
Sable, Lily, and Marx are sent to Darkheather to learn why Overlord Rampaul is recruiting mouse labor. Will they be able to escape with the secrets they uncover?