For nearly a century of solid profitability, Merrill Lynch was the company that brought Wall Street to Main Street, turning tens of millions of Americans into investors. But by the early 2000s, under C.E.O. Stanley O'Neal, it had developed a raging case of Goldman Sachs envy and began a blind stampede into unprecedented risk. In an excerpt from their new book, Bethany McLean and Joe Nocera chart the evisceration of the “Mother Merrill” culture as the firm crashed head-on with the mortgage meltdown.