On July 22, 2011, Anders Behring Breivik detonated a car bomb in downtown Oslo, Norway. He didn't stop there, traveling several hours from the city to ambush a youth camp while the rest of Norway was distracted by his earlier attack. That's where the facts end. But what motivated him? Did he have help staging the attacks? The evidence suggests a startling truth: that this was the work of one man, pursuing a mission he was convinced was just. If...