Shapeshifter Liska is training as a warrior. For Arborven is a city that is under constant threat. Ringed by mountains, the city is held within an enormous tree. In amongst the branches shine strings of lanterns, street lamps and flickering torches. There are temples with turrets and steeples, castles and mansions, bridges of rope and plank wider than any highway strung between them. And Arborven is home to thousands of people. So when Liska overhears a plant to take over the city, and no one believes her, she knows as a warrior it is her duty to act. So with Lug, whose power over earthworms is dismissed as useless, a ghost-girl, Elowen, and an extraordinary kittimew, she goes on an epic journey to defeat the worst threat their world has ever known.