On first meeting him, one might not suspect Alan Grayson of being a crusader against government-contractor fraud. Six feet four in his socks, he likes to dress flamboyantly, on the theory that items such as pink cowboy boots help retain a jury's attention. He and his Filipino wife, Lolita, chose their palm-fringed mansion in Orlando, Florida, partly because the climate alleviates his chronic asthma, and partly because they wanted their five children to have unlimited access to the area's many theme parks.

Grayson likes theme parks, too. Toward the end of two long days of interviews, he insists we break to visit Universal Studios, because it wouldn't be right for me to leave his adopted city without having sampled the rides. Later he sends me an e-mail earnestly inquiring which one I liked best.

He can be forgiven a little frivolity. In his functional home-office in Orlando, and at the Beltway headquarters of his law firm, Grayson & Kubli, Grayson spends most of his days and many of his evenings on a lonely legal campaign to redress colossal frauds against American taxpayers by private contractors operating in Iraq. He calls it "the crime of the century."

His obvious adversaries are the contracting corporations themselves—especially Halliburton, the giant oil-services conglomerate where Vice President Dick Cheney spent the latter half of the 1990s as C.E.O., and its former subsidiary Kellogg, Brown & Root, now known simply as KBR. But he says his efforts to take on those organizations have earned him another enemy: the United States Department of Justice.

Over the past 16 years, Grayson has litigated dozens of cases of contractor fraud. In many of these, he has found the Justice Department to be an ally in exposing wrongdoing. But in cases that involve the Iraq war, the D.O.J. has taken extraordinary steps to stand in his way. Behind its machinations, he believes, is a scandal of epic proportions—one that may come to haunt the legacy of the Bush administration long after it is gone