The Stiehl assassin / Terry Brooks.

The Skaar have arrived in the Four Lands, determined to stop at nothing less than all-out conquest. They badly need a new home, but peaceful coexistence is not a concept they understand. An advance force under the command of princess Ajin has already established a foothold, but now the full Skaar army is on the march - and woe betide any who stands in its way. But perhaps the Skaar victory is not a foregone conclusion. The Druid Drisker Arc has freed both himself and Paranor from exile. Drisker's student, Tarsha Kaynin, has been reunited with the chief defender of the Druid order, and is learning to control her powerful Wishsong magic. If they can only survive Tarsha's brother and the Druid who betrayed Drisker Arc, they might stand a chance of defeating the Skaar. But that is a very big if . . . as Tarsha's brother now carries the Stiehl - one of the most powerful weapons in all the Four Lands - and is determined to take his revenge on everyone who has wronged him.