A fifth of the population of Earth dies at once—why? A plague? Weapons of mass destruction? Or are the little green men to blame? In search of an answer, the heroes—a married couple, a surgeon, and a forensic expert—don’t even rule out such a cause, since the probability of the other versions is no greater. Offering, analyzing, and discarding version after version, the heroes gradually come to a completely different question: why were the ones who stayed alive so lucky? And were they lucky at all?