A serendipitous moment—one when you make a striking and unexpected discovery quite by accident—is the genesis of Mario Vargas Llosa’s most recent novel. A single sentence in a biography of Joseph Conrad aroused his curiosity. “Without you,” Conrad wrote to a certain Roger Casement, “I would have never written Heart of Darkness.” Vargas hadn’t heard that name before. So he began to investigate. The investigation, conducted in three continents, lasted three years. Every bit of information he harvested added to his admiration for a man who had inspired the author of one of the greatest modernist novels.