Outrage mixes with despair in “Dark Waters,” an unsettling, slow-drip thriller about big business and the people who become its collateral damage. It’s a fictional take on a true, ghastly story about a synthetic polymer that was discovered by a chemist at DuPont, which branded it Teflon.

One of those seemingly magical substances of the modern age, Teflon was advertised as an “amazing new concept in cooking,” a 20th-century wonder meant to make life easier. “Choose a pan like you choose a man,” a British ad for a Teflon-coated pan suggested. “It’s what’s on the inside that counts.”

What was inside Teflon, anyway? In “Dark Waters,” the answer starts with cows that belong to Wilbur Tennant (Bill Camp), a West Virginia farmer engorged with rage, whose animals (and livelihood) are horribly and inexplicably dying on his pastoral-looking land. He has his suspicions about the cause, but the deaths are an enigma that becomes a murder mystery that, in turn, opens into a legal inquiry into corporate malfeasance and government accountability. Leading the charge is Rob Bilott (Mark Ruffalo), a corporate lawyer in Cincinnati who defended chemical companies but became an unlikely crusader for the other side when he went up against DuPont.

Opening the story with a spooky prologue right out of the horror handbook, the director Todd Haynes makes it clear that here be monsters: It’s 1975 and a gaggle of young trespassers venture onto fenced-off property to go for a night swim. (The script is by Mario Correa and Matthew Michael Carnahan.) Soon after the swimmers splash into the dark, oily waters (kids do the stupidest things), they are rousted by a booming male voice of authority. Given the horror-film setup, you half expect a creature from this dark lagoon to rise up or a chain-saw killer to buzz into view. Instead, men in a boat marked “containment” glide in, spraying something on the slicked surface.