The Book of the New Sun, by Gene Wolfe.
The premise: set in a brutal medieval world called Urth, a young man named Severian has been raised from birth in the Guild of the Torturers, who dispense justice for the Autarch. Severian is curious, and different, which one day brings about misfortune as he is exiled from the Guild for committing an unpardonable sin: showing mercy to a victim.
So far this book has lived up to its pedigree of being one of the all-time SFF classics. Wolfe is an astounding talent.