Set hundreds of years before the Deptford Mice Trilogy, the story tells the tale of the squirrel-maiden Ysabelle and the bat Vespertilio (or Vesper). The story begins in a ruined tower in London. That is where the bats live, and they are readying themselves to go to war to fight the squirrels. They believe that the Starwife, ruler of the black squirrels, has stolen their birthright of insight and seeing into the future. In the midst of the preparations, Vesper longs to experience the battle for himself, but he is too young to go.