Melting Stones, by Tamora Pierce

Evvy has spent four years off the streets, training as a stone Mage. Now she travels to the battle Islands with the still recovering Rosethorn, and Fusspot, commonly known as Myrrhtide. The People of the islands called Rosethorn, who is a plant mage, and Myrrhtide, a water mage, to see why all their ponds are turning to acid and all of their plants are dying.

Evvy is not a people person and the people on the island are no exception. But when she finds out the root of the problem, she realizes that she may have to save the islands.

This suspenseful novel is full of magic, and is one Tamora Pierce’s best.

P.S. This book uses characters from Tamora Pierce's Circle of Magic Series