Lancelot by Walker Percy, Percy

Lancelot Lamar is a disenchanted lawyer who finds himself confined in a mental asylum with memories that don't seem worth remembering. It all began the day he accidentally discovered he was not the father of his youngest daughter, a discovery which sent Lancelot on modern quest to reverse the degeneration of America. Percy's novel reveals a shining knight for the modern age--a knight not of romance, but of revenge.