ESSEX, N.Y. — Striding barefoot through the fields of his farm in the Adirondacks, S. B. Lewis, known as Sandy, is talking without pause, gesturing this way and that in a soft summer rain.


That Mr. Lewis is in a rage is not unusual. A few days earlier, he had watched as the computerized stock trading of Knight Capital ran amok.


“If Knight blows, six firms follow, and the whole corrupt thing goes up,” he said. “Predator banks and hedge funds run the market for their pleasure — there’s no rational structure, nothing!”


He is just warming up. News reports have revealed a world he knows intimately. Goldman Sachs pays vast fines to avoid prosecution for mortgage securities fraud. Barclays manipulates interest rates. The Senate exposes HSBC as a racketeering enterprise, laundering money for drug cartels. Banks are laden with bad assets.


And Wall Street, Washington, the press corps, everyone sits and stares like so many dumb cows.


“The complicity on Wall Street is sickness!” Mr. Lewis says. He fixes you with his laser stare. “If you think the big firms are being honest” — his tone slides streetwise — “well, sweetheart, go think something else!”


The temptation is to dismiss Mr. Lewis, 73, as a crank, except he once ruled as an eccentric genius of arbitrage, with a preternatural feel for the tectonic movements of the markets. He has railed for decades about venalities now on daily display. Rude truth is his currency.


He knows Wall Street’s heights. He helped hire Michael R. Bloomberg, and he invested the money of two former Securities and Exchange Commission chairmen, making a fortune in the 1980s. And he knows its depths, since he pleaded guilty to stock manipulation in 1989, and was barred from the Street.


President Bill Clinton pardoned him, and a federal court judge later said Mr. Lewis acted out of pure reforming impulse.


But he remains in self-imposed exile.


Mr. Lewis wants to flip over Wall Street’s paving stones and search for worms. He relies on his singular strength: he discerns patterns where most see random data. He forecast the financial meltdown of 2008 that vaporized Bear Stearns, Merrill Lynch and Lehman Brothers. In 2006, he warned a Bear Stearns executive: “Bear is toast. Get out now!”


Lehman Brothers, he notes, certified it was in good health in June 2008 and issued stock, attracting investment, including from the New Jersey Teachers’ Pension and Annuity Fund. Secretly, Lehman was on an intravenous drip, poisoned by bad debt.


“My respect for their brains is too great to think Lehman’s top guys didn’t know they were conveying the cynical impression of health,” Mr. Lewis said.


He is no less suspicious of Goldman Sachs, which has alumni sprinkled across the upper reaches of government. In a tough spot, Goldman obtained extraordinary permission to make an overnight metamorphosis from investment bank to traditional bank holding company.


“Can I prove this was a wired deal? Absolutely not,” Mr. Lewis said. “Am I certain of it? Only 100 percent.”


As for the whirling, three-million-shares-per-second casino of Wall Street? He sees it as rigged. “I would not risk stocks under any circumstances,” he said, “because we don’t know when this thing is going to blow.”


Nothing about Mr. Lewis is easy. He delights in sending scabrous, insulting, free-associative mass e-mails to journalists, financiers and members of Congress. Show annoyance, and he doubles down. “You know what I do with tension?” he said. “I ratchet it up!”


Not surprisingly, some dismiss him as a nut. As striking are those who pay careful heed.


“Sandy’s right; government created a banking oligopoly with no accountability,” said Peter Solomon, a friend of Mr. Lewis’s who runs an investment banking firm.


Arthur Aeder, a retired accounting executive, was twice fired by Mr. Lewis. “Not many antagonize Goldman just for the hell of it,” Mr. Aeder said. “Most people think, ‘I have a family to feed.’ ”


Mr. Lewis is no less harsh on himself. After a visit, he handed us laptops containing every furious e-mail he had sent and received over 10 years.


“The Wall Street ethic broke decades ago,” he said by way of goodbye. “The stink is terrible.”