In 2015, a group of twenty-one young people sued the federal government for violating their constitutional rights by promoting the climate catastrophe, depriving them of life, liberty, and property without due process of law. They Knew offers evidence for their claims, presenting a devastating, play-by-play account of the federal government's role in bringing about today's climate crisis. James Speth, tapped by the plaintiffs as an expert on climate, documents how administrations from Carter to Trump—despite having information about climate change and the connection to fossil fuels—continued aggressive support of a fossil fuel-based energy system.

What did the federal government know and when did it know it? Speth asks, echoing another famous cover up. What did the federal government do and what did it not do? They Knew (an updated version of the Expert Report Speth prepared for the lawsuit) presents the most compelling indictment yet of the government's role in the climate crisis, showing a forty-year failure to take action.

Since Juliana v. United States was filed, the federal government has repeatedly delayed the case. Yet even in legal limbo, it has helped inspire a generation of youthful climate activists.