A corporate defense attorney takes on an environmental lawsuit against a chemical company that exposes a lengthy history of pollution.
In 1998, Robert Bilott (Mark Ruffalo) is a corporate defense attorney in Cincinnati, Ohio. One day at the office, farmer Wilbur Tennant (Bill Camp), an acquaintance of Robert's grandmother, arrives with boxes of videotapes, requesting Robert's assistance. Robert doesn't have time for him, but later drives out to his home town of Parkersburg, West Virginia, to see his grandmother and then Wilbur. Wilbur shows him evidence - from video tapes he's made to remaining cow parts - of how all 190 of his cows have died, showing signs of bizarre and strange disease. He knows it has to do with the huge company DuPont, who has a plant in town, since his brother had been working for them disposing of waste. Robert asks his boss, Tom Terp (Tim Robbins) if he can take the case, assuring him it will be a small side project. Tom reluctantly agrees.
At a function for attorneys, Robert broaches the subject with DuPont attorney Phil Donnelly (Victor Garber), who politely tells him he's not aware of the specifics but will help out in any way he can. Mark files a small suit so he can gain information through legal discovery of the chemicals that have been dumped on the site. He doesn't find anything useful, then realizes it's possible that whatever poisoned Wilbur's cattle could be something that isn't even regulated by the EPA. At an awards dinner, he presses Phil on the issue, who curses at him and calls him a hick. Robert is able to legally force DuPont to turn over its information, which it does, sending him hundreds of boxes of documents hoping he'll never find anything. He goes through the files one by one, finally finding reference to a chemical called PFOA that he can't find anything about. He continues going through the documents.
In the middle of the night, Robert's pregnant wife Sarah (Anne Hathaway) finds him tearing the carpet off the floors and going through their pans. He tells her they're being poisoned, and she thinks he's gone mad, until he explains what he's found in the DuPont documents: PFOA-C8 is a man-made chemical used in the production of Teflon. It was created for army tanks, but then used by companies in American homes. DuPont has been running tests of the affect of it for decades, including on animals and on their own employees. Their own studies show that it caused cancer in animals, people, and birth defects in babies of women working on their line - and they never said a thing. They then dumped hundreds of gallons of toxic sludge upriver from Wilbur's farm.
Wilbur, meanwhile, has been shunned by the entire local community for suing their biggest employer. His house is broken into, and he gets sicker. Robert goes to him with the evidence and tells Wilbur to take the settlement DuPont is offering, but Wilbur refuses, wanting justice and not wanting to stay silent. He tells Robert he and his wife both have cancer. Robert feels guilty, and so he gets Wilbur the settlement, he also writes a brief with all the DuPont evidence and sends it to the EPA and Department of Justice, among others. The EPA fines DuPont $16.5 million.
DuPont sends a letter to Parkersburg residents telling them that there is PFOA in the water but in safe amounts. Darlene Kiger (Mare Winningham) and her husband get the letter and approach Robert, Darlene remembering her first husband's illness while working in the plant that the employees called "Teflon flu". She also had to have a hysterectomy before she was 40. Robert decides to start with the Kigers to lead a class action lawsuit against DuPont - he wants a settlement and also medical management for the people of Parkersburg, meaning DuPont will have to monitor and take care of their health care. There is push-back at a meeting with the partners at the law firm, who think this will ruin the firm's reputation to go after a company that they would normally be defending. Tom angrily chastises them, arguing that this is the right thing to do.
Robert takes the class action to court in Charleston, West Virginia in order to secure medical monitoring, with local attorney Harry Dietzler (Bill Pullman), and since PFOA isn't regulated, they argue that DuPont is liable because the amount in the water was higher than the one part per billion their internal documents argued to be safe. In court, DuPont claims they did a new study that says that 150 parts per billion is safe. Robert is aghast, and the locals begin protesting DuPont and the story becomes national news. DuPont agrees to settle for $70 million. Legally, they are only required to do medical monitoring if scientists prove that PFOA causes the ailments, so an independent scientific review is set up to study the affects of PFOA. If they find in favor, DuPont will have to pay up. In order to get data for it, the firm tells the locals they can get their settlement money after donating blood, and nearly 70,000 people donate to the study.
Years and years go by, with no result from the study. Wilbur passes away, the Kiger family are harassed locally, and Robert faces extreme financial strain, having worked the entire case on the promise of the settlement and continuing to work on it, having to pay scientific experts. He's taken pay cut upon pay cut at the firm, and things are tense with Sarah. When Tom tells him he needs to take another pay cut, Robert collapses, shaking. At the hospitals, the doctors tell Sarah he had an ischemia, or minor stroke, and that he needs to get on new medication and stop dealing with so much stress. Sarah tells Tom to stop making Robert feel like a failure, since he's done something for people who needed help.
Finally, seven years after the panel was convened, the scientific review contacts Robert and tells him that PFOA causes multiple cancers and other diseases. At dinner with his family, Rob is informed that DuPont is reneging on the entire agreement. He is angry, saying Wilbur told him that there wasn't any justice and he didn't believe him. So Rob decides to take each defendant's case to DuPont, one at a time.
A post-script text explains that Rob won his first three multi-million dollar settlements against DuPont, and finally DuPont settles the class action for $671 million. PFOA is still in the blood of 99% of life on earth, and thousands of chemicals are still unregulated.