Book Four of Ursula K. Le Guin's Earthsea Cycle
Years ago, 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 through no choice of his own.
Once, when they were young, they helped each other at a time of darkness and danger and shared an adventure like no other. Now they must join forces again, to help another in need -- the physically and emotionally scarred child whose own destiny has yet to be revealed.