On May 6, 2010, financial markets around the world tumbled simultaneously and without warning. In the span of five minutes, a trillion dollars of valuation was lost. The Flash Crash, as it became known, represented the fastest drop in market history. When share values rebounded less than half an hour later, experts around the globe were left perplexed. What had they just witnessed? Navinder Singh Sarao hardly seemed like a man who would shake the world's financial markets to their core. By the age of thirty, he had left behind London's trading arcades, working instead out of his childhood home. For years the money poured in. But when lightning-fast electronic traders infiltrated markets and started eating into his profits, Nav built a system of his own to fight back. It worked-until 2015, when the FBI arrived at his door. Depending on whom you ask, Sarao was a scourge, a symbol of a financial system run horribly amok, or a folk hero-an outsider who took on the tyranny of Wall Street.