Environmental toxins in the city of Woburn, Massachusetts contaminate the area's water supply, and become linked to a number of deaths of neighboring children. Jan Schlichtmann (John Travolta), a cocky and successful Boston attorney who zips around town in his Porsche, and his small firm of personal injury lawyers are asked by Woburn resident Anne Anderson (Kathleen Quinlan) to take legal action against those responsible.
After originally rejecting a seemingly unprofitable case, Jan finds a major environmental issue involving groundwater contamination that has great legal potential and a couple of defendants with deep pockets. The local tanneries could be responsible for several deadly cases of leukemia, but also are the main employers for the area. Jan decides to go forward against two giant corporations (real-life companies Beatrice Foods and W. R. Grace and Company) with links to the tanneries, thinking that the case could possibly earn him millions, as well as enhancing his and his firm's already considerable reputations.
Bringing a class action lawsuit in federal court, Jan represents families who demand a clean-up of the contaminated area and an apology. However, the case develops a life of its own and takes over the lives of Jan and his firm. The lawyers for the tanneries' parent corporations are not easy to intimidate, a judge (John Lithgow) makes a key ruling against the plaintiffs, and soon Jan and his partners find themselves in a position where their professional and financial survival has been staked on the outcome of the case.