She died of a stroke after an argument over the price of skimmed milk, and the press remembered her as the Witch of Wall Street, a miser in a rotting black dress. She was also the wealthiest woman in America, a self-taught macroeconomic strategist whose fortune would be counted in billions today, and the person who kept New York City solvent during the Panic of 1907. This episode strips away the tabloid caricature to examine the actual math of Hetty Green’s life, from reading stock quotations aloud to her failing-eyed father at age six in whaling-boom New Bedford to keeping the family books at 13.

Sent to New York at 20 with $1,200 to buy a husband-catching wardrobe, she spent $200 on plain clothes and secretly put the rest into high-yield bonds. When her family’s millions were locked in trusts run by male executors, she fought back in a landmark forgery trial, married with an ironclad prenup, and built a contrarian empire on exhaustive research, mountains of liquid cash, and predatory patience. By 1905 she was the largest individual lender in New York City, running her empire rent-free from a desk at Chemical Bank. Then the cash disappeared from the system, and she was the one holding the bucket.

• The trial that put statistics in the courtroom: Harvard mathematician Benjamin Peirce counting pen downstrokes to show a 1-in-2.5-quintillion chance the will’s signature was real
• Her greenback masterstroke: buying the Civil War currency everyone was dumping, then collecting astronomical profits when the government backed it with gold
• The 1885 rupture: a bank freezing her fortune against her husband’s margin-trading debts, and the ruthless boundary she drew after writing the check that freed her money
• The Panic of 1907, when she lent New York City over a million dollars and sat as the only woman in J.P. Morgan’s bailout room, plus the truth behind the amputation and cold-oatmeal myths