The Other Wind: The Earthsea Cycle, Book 6

The sorcerer Alder fears sleep. He dreams of the land of death, of his wife who died young and longs to return to him so much that she kissed him across the low stone wall that separates our world from the Dry Land, where the grass is withered, the stars never move, and lovers pass without knowing each other. The dead are pulling Alder to them at night. Through him they may free themselves and invade Earthsea.
Alder seeks advice from Ged, once Archmage. Ged tells him to go to Tenar, Tehanu, and the young king at Havnor. They are joined by amber-eyed Irian, a fierce dragon able to assume the shape of a woman.