The Tree of Swords and Jewels — C.J. Cherryh

They said that Ciaran Cuilean was fey -- that he had the touch of the Sidhe on him, and on his lands. And it was true. Elvish blood ran in his veins, and he had been to that other world -- that parallel and magical land of Eald, where Arafel, the Lady of Trees, held dominion.

But what should have been a blessing was as much a curse -- for jealousy and fear grew in the lands of men. Shadows of newly awakened evil swarmed across both landscapes threatening to bring the clang and reek of war from the warm hearthstones of the mortal keeps to the silvery heart of Ealdwood. And Ciaran knew that he must once again put his humanity aside and reclaim his haunted weapons from the Tree of Swords or see both his worlds fold into darkness!