On October 1, 2013, the U.S. government brought down Silk Road-the notorious "Amazon of drugs"-a Dark Web empire where anyone could buy illegal narcotics and pharmaceuticals with the click of a button. Its mastermind, twenty-something Ross Ulbricht, was sentenced to life in prison. So were the site's administrators, moderators, and key players. All except one: a Spanish doctor known only as Doctor X. Who was this phantom figure at the heart of the world's largest online drug bazaar? Why did he escape justice when everyone else fell? And how did a mysterious medic become the Dark Web's most...