Summer - The Guardians of Magic, #4

As the true identity of the threat to the Guardians reveals itself, they realise how big of a challenge they now face. Determined not to give up, Shumuti leads the others on a desperate journey for knowledge; one that will lead them to uncover ancient secrets about the nature of Magic itself. But their enemies have plans as well, and it may already be too late to prevent them from unfolding.  Summer is the final book in the Guardians of Magic series.