"So why is it cool to meld detective stories, where things add up, and science fiction, where they (typically) don't? The melding has been around for decades now, even before the first Blade Runner. Maybe 'cause when they meld, those lousy prognostications might finally make some sense? Call it Space Noir? Which brings me to Hadrian's Fall, Ian Roumain's astonishingly imaginative novel, set on Mars and with one of the best opening lines since...