On May 6, 2010, the US stock market lost nearly a trillion dollars in value in under forty minutes — then mysteriously recovered almost all of it before the closing bell. The culprit wasn't a hacker, a foreign government, or even a rogue algorithm doing something unexpected; it was a perfectly ordinary trading system doing exactly what it was designed to do, just at the absolute worst moment. This week we pull apart the Flash Crash to reveal how the plumbing beneath our financial markets is a patchwork of decade-old assumptions that can unravel faster than any human can react.