“The Mississippi Bubble” was a wild, giddy, devastating, international episode in eighteenth century French and American history that ought to be better known, if, as nothing else, a cautionary tale. At its simplest, a Scottish fugitive named John Law convinced the rulers of France to let him use France as a laboratory for his economic theories, and one of his schemes was selling shares for a new colony in America, eventually centered around what was to become New Orleans. The sales pitches weren’t tethered to reality, especially as the scheme got more and more out of hand. Costain does a good job of following the twists and turns and tyrannical moves that were put in play to try to prop things up...