Tehanu: The Earthsea Cycle, Book Four

Years before, they had escaped together from the sinister Tombs of Atuan - she an isolated young priestess, he a powerful wizard. Now she is a farmer's widow, having chosen for herself the simple pleasures of an ordinary life. And he is a broken old man, mourning the powers lost to him not by choice.

A lifetime ago they helped each other at a time of darkness and danger. Now they must join forces again to help another - the physically and emotionally scarred child whose own destiny remains to be revealed.