The Brothers Karamazov

Old Fyodor Karamazov is a drunken, lecherous, contemptible man - and someone has finally killed him. Of his three sons, one is a passionate soldier who publicly swore to do it, one is a tormented intellectual who may have willed it into being without lifting a finger, and one is a gentle novice caught helplessly between his brothers. Dostoyevsky's final and greatest novel uses a single murder investigation to stage an argument that spans the existence of God, the nature of free will, and whether love or reason can ever truly save a broken family.
Vast, philosophical, and shockingly suspenseful for a book so concerned with the soul, it is widely considered among the greatest novels ever written. Few books ask bigger questions. None answer them with more human weight.