The novel, about the unlikely loves that bloom when terrorists spring out of the air-conditioning ducts of a South American mansion to take a birthday party and an opera singer captive, is currently sweeping all kinds of book clubs, including that of the Arizona Daily Star newspaper. Madison, Wis., is making “Bel Canto” the official book selection for the whole city. A series of prizes helped galvanize sales: the book won the PEN/Faulkner Award and was a finalist for the National Book Critics Circle Award. But such explosive success is still hard to explain, since so many brilliant books die on the shelves. “Every now and then something lines up in the stars,” says Patchett. “There’s just no rhyme or reason to it.” Of course, anyone who’s read her book and loved it would say its success makes perfect sense.