How the FBI built the most powerful—and least accountable—domestic intelligence operation in American history, exposing how the post-9/11 era of surveillance and entrapment left the Bureau vulnerable to the authoritarian forces now reshaping it.

For over a century, the FBI has stood at the center of America’s response to extremism and political violence, identifying threats before they emerge. But what happens when an institution tasked with detecting extremism begins to see threats everywhere?

Investigative journalist Trevor Aaronson traces a country where perceived enemies have only multiplied, and where the Bureau itself may have become one. Through a series of interlocking stories spanning two decades, he follows figures caught between their own hungers for meaning and the government’s need to identify threats: a convert who journeys from the U.S. to the battlefields of Syria; an informant paid to push a plot he cannot control; former FBI agents consumed by institutional distrust; and Kash Patel, a political loyalist who rises to lead the Bureau itself.

As these worlds collide and Aaronson is drawn into the story he set out to report, Bad Guys reveals how Americans drift toward extremism, how investigations shape the people inside them, and how the FBI has begun to gravitate toward the extremism it was built to confront.