Assigned to do some paperwork on what looks like a trivial pro bono case, Erin stumbles upon a hidden epidemic. Dozens of residents in nearby Hinkley have fallen victim to multiple tumors, degenerative organs, and other freak afflictions, yet no one has surmised that the wave of catastrophic illness might have something to do with Pacific Gas & Electric, the industrial plant on the edge of town. With little to go on but her gut, Erin learns that PG&E has employed a deadly form of chromium as an antirust agent, thereby contaminating the local water supply.
Why does Erin alone see through the company's lies? Mostly because of how torn up she is over the victims. She's wounded by their plight, especially that of the tremulous, naive Mrs. Jensen (played with touching vulnerability by Marg Helgenberger). The result is that her investigation never feels overtly noble or righteous; it's a matter of sheer empathetic will.
''Erin Brockovich'' is based on a true story, but almost everything in it feels familiar from previous corporate malfeasance thrillers like ''A Civil Action.'' The movie is consistently engrossing, never quite exciting. Its surprise -- and its pleasure -- is the plainspoken humanity of its outrage, its utter absence of demagoguery and hype. The arc of the tale may be conventional, but Roberts, in her most forceful dramatic performance, allows us to take in every moment through fresh, impassioned eyes.
Erin and Ed become tag team detective partners, and it's a delight to watch Roberts, with her flirtatious sparkle and undertow of melancholy, ricochet off Finney's wonderfully jaded, dry as beef jerky performance as the beleaguered career attorney who knows too much about the loopholes of his profession to have much faith left in it. As George, the biker next door who becomes Erin's lover after he begins to look after her kids, Aaron Eckhart, swathed in tattoos and an overgrown foliage of goatee and sideburns, may be playing a bit of an ideal -- a rebel/hunk/househusband -- but he makes goodness as palpable as he did yuppie evil in ''In the Company of Men.''
In a sense, the film's ultimate villain is the bureaucratic impersonality of the legal system. Ed doesn't think that his firm has the financial resources to win the case, and so he brings in a couple of expensive, big shot lawyers (Peter Coyote and a rather too caricatured Veanne Cox) to help shoulder the burden. The ultimate weapon, of course, is Erin herself; she's the only one who cares enough to bother winning the trust of the plaintiffs.
''Brockovich'' can be as foursquare inspirational as a Capra film (the smoking gun that finally indicts PG&E practically drops out of the sky), but director Steven Soderbergh has made it with the sort of gentle, unfussy confidence that allows him to throw away the movie's culminating moment on a quiet front porch. This is a muckraker that hums with decency.