Following the shocking events at Icegaard, Phoenix and her friends gather with the Hunters, desperate to unite the warring clans before their enemy, the Master, launches his attack on Ember. The Cavern of Light offers hope in the form of a legendary weapon, but the friends must brave the unknown, facing down new and deadly creatures in search of the artifact that could save their world. As an epic final showdown draws near, Phoenix is determined not to lose anyone else that she loves. But the Master is more brutal and powerful than she ever imagined, and as Phoenix's past and present collide, unthinkable sacrifices will have to be made to defeat him.