Lockhaven burns. Gwendolyn, leader of the Mouse Guard, rots in a weasel prison. Across the territories, weasels run wild, and the only cities that remain safe have taken to extreme measures to protect the mice within their walls. Treachery and greed have finally upset the tightrope-balance of the mouse civilization, and wild beasts now roam between towns, not held back by the scent border that has protected them for generations.
In secret, though, a small group of Guardmice refuse to believe that all is lost, and plan an expedition to recover the one person that may offer a sliver of light – however hopeless – to the few remaining free mice. Maybe, just maybe, if Gwendolyn can be rescued, the Mouse Guard may live to fight another day.