It was an ordinary day at his Los Angeles law office when John Nadolenco opened a letter from Brazil enlisting his help in a mission to retrieve a stolen, and quite possibly cursed, 836-pound emerald. The year was 2014, the heyday of the Nigerian prince email scam, and the up-and-coming attorney was no fool. “I immediately thought it was just completely fake, a total hoax,” he said. “I was like, ‘I’m not falling for this one. I’m smarter than this.’” He tossed the letter in the trash. But Nadolenco’s boss asked if, as a favor, he could look into the...