FORTUNE -- At about 9:30 p.m. on Tuesday, October 25, David Schamis, a director of a once-obscure futures brokerage company called MF Global, placed a call to his friend, Jacob Goldfield.

Goldfield, 52, was a former trading superstar who had spent 15 years at Goldman Sachs—brilliant and impeccably connected (Bob Rubin and Larry Summers loved him), but equally quirky and unassuming. Raised in the South Bronx, he'd majored in physics at Harvard before dropping out of law school there to start at Goldman, where he made partner in record time.

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