A reasonably clever, utterly underhanded variation on that durable paranoia set-up most familiar from the school of Hitchcock: X goes home one day--nobody knows him. X this time is (he thinks) Londoner John Tiverton, metallurgical researcher, and he tells his story with calm, irony, and logic, admirable qualities indeed when a man is denied by wife, mother, mistress, neighbors, and colleagues; they all swear that John Tiverton died six months ago and bore no resemblance to our narrator. (His daughter, however, says, ""Hallo daddy."") He tries to figure it out. Assuming he is Tiverton--did he have plastic surgery? Assuming he isn't--he finds himself using the name ""Charles Thomas""--perhaps he was trained to impersonate Tiverton (a possessor of defense secrets) in a pseudo-defection scheme and got carried away in the role. That's the theory that Mr. X pursues, but the answer, of course, is none-of-the-above, as you'll ruefully discover if you let yourself be tricked into sticking around for a denouement that may remind you, in a pale, pale way, of The Murder of Roger Ackroyd.