Edward Snowden touched off a global debate in 2013 when he gave Barton Gellman, Laura Poitras and Glenn Greenwald each a vast and explosive archive of highly classified files. For Gellman, that was only the beginning. He jumped off from what Snowden gave him to track the reach and methodology of the U.S. surveillance state and bring it to light with astonishing new clarity. Along the way, he interrogated Snowden's own history and found important ways in which myth and reality do not line up. Dark Mirror is the story that Gellman could not tell before, a gripping inside narrative of investigative reporting as it happened and a deep dive into the machinery of the surveillance state. Gellman recounts the puzzles, dilemmas and tumultuous events behind the scenes of his work. This is a compelling portrait of national security journalism under pressure from legal threats, government investigations, and foreign intelligence agencies intent on stealing Gellman's files.