3rd in the "Runestaff" series, featuring Dorian Hawkmoon. The Dark Empire had grown so strong that the people of Kamarg sought escape by warping their country into another dimension. Hawkmoon knew such sanctuary would only be temporary, and was fated to don sword and armor again... in a strange and unfriendly land (which I think is an alternate America.) The original 4 Hawkmoon books are my favorites by Moorcock, and I strongly recommend them.