Robin Sloan's 2012 novel, Mr Penumbra's 24-Hour Bookstore, was as strong a debut as you could ask for, an instant geek classic of bibliophilia, magic and technology; now, with today's release of Sourdough, Sloan returns to the alienated, quirkily funny and brilliant lives of technology workers, in a tale of food, the flesh, novelty-seeking, ancient tradition, and immortal colony-organisms.