Martin Harris returns home after a short absence to find that his wife doesn't know him, another man is living in his house under his name, and the neighbors think he's a raving lunatic. Worse, not a single person - family, colleague, or doctor - can vouch for him. Worse still, the impostor shares all of Martin's memories, experiences, and knowledge, down to the last detail. He is, in fact, a more convincing Martin than Martin himself. Is it a conspiracy? Amnesia? Is Martin the victim of an elaborate hoax, or of his own paranoid delusion?