Richard Powers says his new novel, Orfeo (W.W. Norton & Co.), reveals that there's little difference between a passion and an idea. The book is about Peter Els, a retired composer trying to recover his lost muse at the end of his life. When Els combines this search with his second passion, for home microbiology, he inadvertently sets off the alarms of Homeland Security and becomes the target of a nationwide manhunt. Powers discusses the slow "germination" of ideas behind this cutting-edge story of musical microbiology, and the rival versions of modernity that its main character has spent his artistic lifetime trying to reconcile.