The Devil We Know investigates the toxicity of perfluorooctanoic acid--PFOA/PFA, also known as C8--the key ingredient found in non-stick cookware, stain resistant furniture and carpets, wrinkle free and water repellent clothing, cosmetics, lubricants, paint, pizza boxes, popcorn bags, and many other everyday products. The film centres on Parkersburg, West Virginia, in the United States, at the DuPont facility that manufactured Teflon, and dumped at least 1.7 million pounds of PFOA into rivers and streams between 1951 and 2003, knowing that it was a carcinogen. The film follows the personal stories of several people who worked at the facility that experienced cancers and birth defects, and also reveals the detection of PFOA in the blood of more than 98% of the general US population in the low and sub-parts per billion (ppb) range, with levels much higher in chemical plant employees and surrounding subpopulations.