Alan Moore, author of Watchmen and V for Vendetta, has written a short story for his magazine Dodgem Logic. It's been published online by The New Humanist. It's pretty good, though the ending seems signposted from about a mile out. The only thing that confuses me is that I'm not sure that the New Humanist describes it as a "chilling rationalist short story" and I'm not really sure that it's 'rationalist' at all. It's a quick, entertaining read though.