Circle of Thieves — C. Greenwood

In the wake of a painful betrayal, Ilan abandons her friends among the river people to return to the peace of shadowy Dimmingwood. But things in the forest are not as she left them. A deadly new enemy is attacking the local villagers, threatening the very existence of the forest outlaws. When Ilan mounts a rebellion against Rideon the Red Hand, the brigand camp is divided between those loyal to their old captain and those prepared to follow Ilan in a war against the mysterious magical raiders.