The Order of Chaos — Jennifer Jenkins

When Ana fails at her duties as a tree guardian, she opens the door for dark magic to take hold of the Mother Tree--the source of all magic in the region. An evil force moves throughout the Lingering Sea and no witch is safe. Ana must turn to Carlo, the grandson of her best friend and missing key to saving the tree. Unfortunately, Carlo's sanity sits on a razor's edge and may lead to the salvation or destruction of all magic. The solution sits firmly between order and chaos.