On an unseasonably warm October morning, Joe Mendelson, an idealistic young lawyer working on a shoestring budget for an environmental organization no one had heard of, hand-delivered a petition to the Environmental Protection Agency asking it to restrict greenhouse gas emissions from new cars. The Clean Air Act authorized the EPA to regulate "any air pollutant" that could reasonably be thought to endanger public health. But could something as basic as carbon dioxide really be considered a harmful pollutant? And even if the EPA had the authority to regulate emissions, could it be forced to do so?

The Rule of Five tells the dramatic story of how Mendelson and the band of environmental activists and lawyers who joined him carried his case all the way to the Supreme Court. It reveals how accident, infighting, luck, superb lawyering, politics, and the arcane practices of the Supreme Court collided to produce a legal miracle. The final ruling in Massachusetts v. EPA, by a razor-thin 5-4 margin brilliantly crafted by Justice John Paul Stevens, was a landmark victory that paved the way to important environmental safeguards which the Trump administration fought hard to unravel and the Biden administration seeks to restore and expand.