The sequel to Ursula K. Le Guin's A Wizard of Earthsea and "The Tombs of Atuan". In A Wizard Ged was 15-18 years old. In Tombs he was a secondary character, but he was perhaps 35-40. And now, he's become archmage of Roke (as mentioned at the end of the first book), and I would guess between 55 and 60 years old. The book starts with the prince Lebannen from Enlad coming bearing the news that there are rumours that magic is failing in the Reaches. Ged sees something in Lebannen and Lebannen worships the ground that Ged walks on (this isn't particularly well played by Le Guin), so the two set out on a archipelago-spanning journey to try to find the cause of the problem.
Much of the book is about dealing with the fact that you will eventually die - no one lives forever. Ged is apparently the only person in the world who truly believes this, and those that don't believe are all being influenced by ... something.
While I enjoyed revisiting the single greatest hero of my childhood (Ged), this is definitely the weakest of the three books in the initial trilogy (Le Guin wrote these three in a clump around 1970, but would after 1990 revisit it with a couple more novels and some short stories). It's heavy-handed and pedantic in its lessons about accepting what we've been given, and the story has little joy or pleasure in it.