Fool's Errand — Robin Hobb

For fifteen years FitzChivalry Farseer has lived in self-imposed exile, assumed to be dead by almost all who once cared about him. But that is about to change when destiny seeks him once again. Prince Dutiful, the young heir to the Farseer throne, has vanished and FitzChivalry, possessed of magical skills both royal and profane, is the only one who can retrieve him in time for his betrothal ceremony--thus sparing the Six Duchies profound political embarrassment...or worse. But even Fitz does not suspect the web of treachery that awaits him or how his loyalties to his Queen, his partner, and those who share his magic will be tested to the breaking point.