Snowden's Box. Dale Maharidge

      In the spring of 2013, an unauthorized trove of NSA files traveled nearly 5,000 miles in the care of the US Postal Service.

      Postmarked May 10 at a former pineapple plantation village on the island of Oahu, the box of secrets soared east over the Pacific Ocean in a small flat-rate box, bearing a stamp for $5.80. It traversed the breadth of America before landing, unceremoniously, on the fourth floor of a nondescript walk-up apartment building in Brooklyn.

      The sender had shipped the box via Priority Mail. He’d addressed it to a person he’d never met at a home he’d never seen. The recipient, in turn, knew nothing about him or the contents of the box. Her job was simple: carry it to a third person, who would ferry the package to its final destination.

      At the time, to the best of the sender’s knowledge, no one was paying attention.

      By the first week of June, the whole world was watching. Secrets began streaming out of the box, onto the front pages of newspapers. They included evidence that the US government had created a massive surveillance apparatus and used it to spy on its own people. Intelligence officials blasted the unidentified source of the leaks and, warning of dire consequences, prepared to launch a criminal probe.

      But before anyone could unmask him, the leaker revealed himself. The cover of the Guardian bore a giant yellow headline: “The Whistleblower.” Below it appeared a photo of Edward Joseph Snowden. The twenty-nine-year-old had a patchy goatee and an earnest expression. He wore rectangular, semi-rimless Burberry eyeglasses — these would soon become iconic — with the left nose pad inexplicably missing. He identified himself as an NSA infrastructure analyst working for the defense contractor Booz Allen Hamilton.

      The materials he’d taken, Snowden told reporters, revealed “an existential threat to democracy.”

      “I don’t want to live in a world where there’s no privacy and therefore no room for intellectual exploration and creativity,” he added.

      In the years that followed, Snowden’s story would be told and retold, a ballad for our times. The saga unfolded in films, including Laura Poitras’s Oscar-winning documentary Citizenfour and Oliver Stone’s biopic Snowden, and in such books as No Place to Hide by Glenn Greenwald, Luke Harding’s The Snowden Files, and, most recently, Snowden’s own memoir, Permanent Record.

      Missing from those chronicles so far has been a small but crucial episode — the journey of a plain cardboard box that passed through strangers’ hands, setting the rest of the story in motion. In its absence grew a question: if the American government’s surveillance was so mighty, so all-seeing, how did a motherlode of classified information get spirited away by mail, right under the watchers’ noses?

      The answer may be simpler than you think.

      The story of Snowden’s box is deeply human, somewhat messy, and more than a little weird. It’s about a brief moment when strangers worked together to build an underground railroad for secrets — a