The never-before-told inside story of the high-stakes, four-year-long investigation into Donald Trump’s Russia ties—culminating in the Steele Dossier, and sparking the Mueller report—from the founders of political opposition research company Fusion GPS. What began as a march through a mind-boggling trove of lawsuits, bankruptcies and sketchy overseas projects soon took a darker turn: The deeper Fusion dug, the more it began to notice names and patterns that Simpson and Fritsch had come across during their days covering Russian corruption—and the more it became clear that the focus of Fusion’s research going forward would be Trump’s entanglements with Russia.