Chaos Unleashed: (The Chaos Born 3) by Drew Karpyshyn
The Legacy, a magical barrier protecting humanity from Chaos, has crumbled.
Four unlikely champions, each touched with Chaos magic at birth, are all that can stop the return of Daemron the Slayer. Armed with the Talismans of power the four champions, the Children of Fire, must find the Keystone, a fabled place where, or so it is said, the Legacy can be restored.
But even the noblest heart can be twisted by the tainted magic of Chaos...