“So you think it had to do with the way the film was marketed,” said Charlie Rose in 2000—the glory days of that eponymous show, when Rose was still empowered to ask the questions, rather than being subject to them. His guest was Michael Mann, whose film, the whistle-blower thriller The Insider, was a confirmed letdown at the box office.

And not for lack of good press. The film had gotten good press: a 3.5-star review from Roger Ebert, and kind words from the likes of Janet Maslin, at the New York Times, who called it “Mann’s most fully realized and enthralling work,” praising the “pulse-quickening panache” of the auteur’s rigid but rich direction.

The film certainly wasn’t a flop for a lack of recognizable names on the marquee, either, to say nothing of the fact that this is a ripped-from-headlines story that the film’s primary market, the American news-watching public, ought to have known: that of Jeffrey Wigand, the biochemist who in 1996 took to 60 Minutes to blow the whistle on the “big seven” tobacco company Brown & Williamson. On a February 4 episode of the CBS program that year, Wigand revealed, among other things, that B&W had been using ammonia and other chemicals to increase the effect of nicotine in its cigarette products.

This information was no doubt relevant to a public whose consumption of cigarettes had catapulted the tobacco industry into an indomitable social and political force, a mover and manipulator of laws because it had by then became a master mover and manipulator of money and public image. As The Insider depicts, getting this news out to the public, in defiance of that industry, would result in Wigand becoming one of the most significant whistle-blowers of the century.

The Insider, cowritten by Mann and Eric Roth (Forrest Gump, Munich, The Good Shepherd, and Mann’s Ali), turns 20 this week, and it’s as alive with style and possibility as it ever was. It chronicles the slow process of convincing the altogether principled and extraordinarily loyal Wigand to go against his confidentiality agreements—gag orders signed upon his firing from B&W—to catch the tobacco industry in a dangerous lie relevant to public health. The film darkly but energetically depicts the battle lines that are immediately drawn at CBS, as 60 Minutes producer Lowell Bergman fights the powers that be to keep this story on the air, and in Wigand’s own life, as his marriage, lifestyle, and psychological well-being are thrown topsy-turvy by a powerful tobacco industry keen on striking back.

So: a David and Goliath story. A story about doing the right thing and suffering the consequences of power—about putting it all on the line. This being a Michael Mann feature, it’s also a study of manhood, of course, and in this case, of having a moral backbone. Two men—Wigand and Bergman—are fashioned into heroes for their willingness to manipulate the law and the press, to say nothing of risking their livelihood, for the sake of their own principles. But these are troubled, imperfect heroes. They get run through the wringer, accordingly.

It’s a story that practically writes itself, in other words—but which, in the hands of a director this precise working with a cast this fiery and alive, more than benefits from the glossy largesse of a Hollywood movie. Al Pacino stars as Bergman, flanked by Christopher Plummer as the legendary journalist Mike Wallace, Philip Baker Hall as pioneering 60 Minutes creator Bob Hewitt, and more. Gina Gershon, Bruce McGill, Diane Venora, and on and on.