The Island of the Day Before

Roberto della Griva, a 17th-century Italian nobleman, is the sole survivor of a shipwreck during a fierce storm. He finds himself washed up on an abandoned ship in a harbour through which, he convinces himself, runs the International Date Line (roughly 180° longitude). Although the shore is very close, Roberto is unable to swim, and is therefore stranded on the ship. He begins to reminisce about his life and his love. He becomes obsessed about his allegedly evil twin brother, who is split from his own persona through a process reminiscent of the doppelgänger effect, and thus accusing him of all the bad things that happened in his life. The brother takes blame mainly for his bad choices and is present to sweeten the disappointments of life. Through this reminiscence he becomes convinced that all his troubles will end, if only he can reach the land. The story is told from the point of view of a modern editor who has sorted through the man's papers. Exactly how the papers were preserved and eventually handed down to the editor remains a point of conjecture.

This work contains references to Eco's previous novels. In one example, there is a mention of a crucial plot point from Eco's first novel The Name of the Rose.