Editor's note: A version of this story was originally published March 27, 2018. It's the end of the workday in Charlotte, and a crowd of bankers and business people is heading home for the day, striding down a plain, ordinary sidewalk next to a nondescript brown building on Trade Street. What these business people perhaps don't know is that just below their feet, about a story or two down, is a bustling underground operation and a steel-encased vault containing billions of dollars in cash.