As London shivers in the grip of an icy blizzard, the Deptford Mice huddle indoors, telling ghost stories to keep the bitter cold at bay. Little do they know that this is no ordinary winter. Their most fearsome enemy has returned from beyond the grave. He plans to use his evil sorcery to plunge the world into an eternal, freezing night, and at his command the bloodthirsty rats of the sewers are stirring once more.

Alone and seemingly powerless in the face of this most terrible of foes, the mice are close to giving up hope. Can they draw on their last reserves of strength to defeat Jupiter one final time, or is it already too late?