Roberto de la Grive is an Italian nobleman who becomes "the only being of our species to have been cast away on a desert ship." The other important characters in The Island of the Day Before are his various teachers, his alter ego, Ferrante, and the women he loves.

As a child, Roberto experiences a delusion that will affect his life for many years: He imagines that he has a bastard brother who hates him and is always trying to do him mischief.

Roberto only rids himself of the specter of "Ferrante" by making him the male lead in a piece of fiction and killing him off — and that in turn is possible only because he finally realizes that Ferrante is a projection of unfulfilled parts of his own psyche.

That psyche has been through the wringer in his short life. He is drawn to male teachers...