What happens when someone infiltrates extremists’ safe spaces? Proudly leftist journalist Talia Lavin knows. Long the subject of their hate and death threats, Lavin posed as an “incel,” an involuntarily celibate boy, in a chat room rife with misogyny and self-pity. She also crafted profiles for a “blonde, gun-toting Iowan” seeking love letters from suitors on a white-supremacist dating site and an “Aryan Queen” on a neo-Nazi propaganda platform. As she witheringly reports on what extremists say when they think they’re alone on the type of websites that have in recent years inspired real-world violence, Lavin also delights in corrupting their world: “I had made their worst nightmares come true,” she writes. “Behind the beautiful Aryan they desired was a fat, cunning Jew, biding her time.”