One day in the spring of 2013, a box appeared outside a fourth-floor apartment door in Brooklyn, New York. The recipient, who didn't know the sender, only knew she was supposed to bring this box to a friend, who would ferry it to another friend. This was Edward Snowden's box - materials proving that the U.S. government had built a massive surveillance apparatus and used it to spy on its own people - and the friend on the end of this chain was filmmaker Laura Poitras. Thus the biggest national security leak of the digital era was launched via a remarkably analogue network - the US Postal Service. This is just one of the odd, ironic details that emerges from the story of how Jessica Bruder and Dale Maharidge, two experienced journalists but security novices got drawn into the Snowden story as behind-the-scenes players.