A mouse's life is short, and the change of seasons can bring many transformations. Since the rebellion of the mouse dissident Midnight in the autumn of 1152, the land has been covered by a thick blanket of snow. Winter has arrived, bringing with it a dangerous food shortage that threatens the beleaguered mouse city of Lockhaven. The mouse guardians Saxon, Kenzie, Lieam, Sadie, and the gray-furred Celanawe are sent on a diplomatic mission to the remote mouse colonies in search of supplies and medicine for the endangered Lockhaven. However, it is not just the icy weather that makes the journey a risky endeavor. Hungry predators are hunting the small rodents on and over the snowy passes between the mouse villages. Spring seems a lifetime away, and not all of the mouse guardians will survive to see that season.