THE FRONT FOR THE DEFENSE OF THE AMAZON, like any progressive group whose name includes front and defense, is a no-frills outfit with ample supplies of devotion and very little clout. Its opponents are, in size and power, what elephants are to gnats. They include Chevron Corporation, the United States government, the armed forces of Ecuador, and the insatiable global demand for oil. (This is a partial list.)

The Frente, as it's known, is based in Lago Agrio, a gritty oil town of 35,000 in northeastern Ecuador's humid, jungly Oriente region, in a second-floor warren outfitted with furniture the Salvation Army might reject. As a gnat, the Frente measures success in humble terms René Descartes would understand: We survive, therefore we are. But something funny is happening on the way to the glorious defeats that would seem to be its destiny. The group has a fighting chance of winning a landmark environmental-damage lawsuit against Chevron, one that could cost the conglomerate an estimated $6 billion in cleanup expenses. The suit was brought by 48 Oriente inhabitants on behalf of 30,000 fellow residents of the oil-rich region—members of the Cofán, Secoya, and other tribes, as well as settlers who arrived in recent decades. The plaintiffs allege that, between 1964 and 1992, Texaco (which merged with Chevron in 2001) dumped 18 billion gallons of toxic wastewater into an area the size of Rhode Island—a brew that allegedly included 18 million gallons of oil, nearly twice the amount spilled by the Exxon Valdez in 1989.

According to the suit, Aguinda v. ChevronTexaco (the first plaintiff listed is Maria Aguinda, a Quechua Indian), the pollution has poisoned the earth, rivers, and air, causing miscarriages, birth defects, and cancer rates three times the national average. Cows and chickens have reportedly dropped dead; fish have gone belly up. Mothers and children walking on the oil-soaked dirt roads, the plaintiffs say, have to wash their feet in gasoline just to remove the gunk.

This isn't the first time a multinational has been accused of egregious misconduct in the Third World, but it is the first time a class-action-style environmental lawsuit this large has gone so far. Originally filed in a New York federal district court in 1993, the suit went through nearly a decade of pre-trial maneuverings that came to a halt in 2002, when a federal appeals court ruled that it had to be heard in Ecuador rather than the U.S.

At first, that looked like the end. Nobody thought Ecuador would hear the case; trials this complicated had never been held there, and the government in Quito was still relatively friendly to U.S. business interests. But in Ecuador, as in many developing countries in Latin America, such governments have been replaced by a new generation of left-leaning nationalist regimes. With popular sentiment shifting, proceedings opened in Lago Agrio's superior court in October 2003, less than six months after the suit was filed. Now, finally, resolution is in sight. The verdict—which will be decided by a single judge rather than a jury—is expected sometime next year.

On a muggy morning in October 2005 in the Frente's ramshackle offices, one big reason for the group's improbable success was standing in front of me. The chief American legal adviser in the case, Steven Donziger, was turning the office into a political stage by doing what he does best—plotting, joking, shouting, defaming, and, in general, behaving like Don Quixote with a Harvard law degree. At 45, Donziger is an imposing figure, with a six-foot-four physique and a face like George Clooney crossed with an Easter Island head. He was fulminating against Chevron for blocking a judicial inspection of the Guanta processing station, outside Lago Agrio, one of 122 allegedly toxic sites originally slated to be inspected in the case.

Under Ecuadorean law, the judge personally investigates evidence. In this dispute, that means making dozens of field inspections, which entail a traveling circus of lawyers, security guards, witnesses, journalists, and separate teams of experts for the judge, plaintiffs, and defendant—all jawing and sample-taking outdoors in whatever weather conditions prevail. The night before the Guanta inspection, Judge Efraín Novillo Guzmán had declared a postponement after Chevron's representatives said they'd been warned of potential violence by locals angry about the pollution. The delay seemed like a good idea for the oil company, in part because the Frente had lured a busload of Ecuadorean journalists out to Lago Agrio, a six-hour drive from Quito over narrow mountain roads. With no inspection, there would be nothing to write about.

But Donziger is savvy enough to spin a sunny day into a hurricane. He worked the phones in nonstop interviews, accusing Chevron's lawyers of everything from cowardice to genocide. When he went live with Paco Velasco—Ecuador's most popular radio talk-show host and, like Donziger, a fountain of addictive outrage—it was a meeting of like-minded vocal cords.

"Texaco doesn't respect the life of Ecuadoreans!" Donziger fumed in gringo-accented Spanish. "They are against the people. They are lying. People have died and people will continue dying because of the pollution!" Donziger was on a roll and he knew it. When the interview ended, he turned to an Ecuadorean activist and said, "That was good, wasn't it?"

In the next room, several young Ecuadoreans were making posters: TEXACO IS COWARDLY AND RACIST! TEXACO IS AFRAID! Down the hall, plans got under way for a day of protest; several dozen indigenous women, looking sullen but photogenic, would wave the posters in front of city hall. Meanwhile, Donziger was firing up the crew of journalists for a gonzo tour of the Guanta site, official inspection be damned. I wouldn't have thought it possible to pity a multinational oil conglomerate that has gotten its way worldwide since 1911, one that made $14 billion in profits in 2006 alone. But watching Donziger stir things up, I almost felt sorry for Chevron.