Weilheim is a cozy Bavarian village, where geraniums drip from window boxes and onion-domed churches and Alpine chateaus line the cobbled streets. Journalist Erich Schmidt-Eenboom lives in this sleepy town, and he was there sifting through files on a warm day in May 2005 when his doorbell rang. On his stoop stood a graying man with his hands shoved in the pockets of his jeans. The man said he was a retired agent from Germany’s spy agency, the BND, and he had pressing news.

Schmidt-Eenboom was used to people with secrets knocking on his door. He had spent more than a decade reporting on intelligence matters, and had written a tell-all book on the BND called Sleuthhound Without a Nose. By now, he was the go-to man for people with dirt on the agency.

So without a second thought, he climbed into the stranger’s car and they drove to the banks of the Ammer River. They stood for a moment soaking up the scenery — the thick meadows, the craggy Alps hovering in the distance. Then the stranger dropped his bomb. “My job was to spy on you,” Schmidt-Eenboom recalls him saying.

A chill crept over the author as he listened to the man describe the lengths the BND had gone to during the three years it spied on him in the 1990s. At times, a shadow entourage of up to fifteen agents had tailed him and his secretary. Family outings, trips to the sauna — nothing was off-limits. The agency had even parked a white VW Golf with a camera in its visor outside his office in downtown Weilheim, and installed cameras in the attic of an old building across the street. These were used to snap photos of his visitors’ license plates. The aim of the program, called Operation Emporio, was to find out who at the BND was giving the author information.

Schmidt-Eenboom didn’t want to believe what he was hearing. But the stranger knew things only a spy could: The hodgepodge of papers and clothes the author used to keep in his trunk; the way his secretary would buy pork cutlets at the market across the street, and then wolf them down as she walked back to the office. “There was no doubt he was telling the truth,” Schmidt-Eenboom says. “The only question was whether they had gotten my sources. And if they had, I might as well retire.”

So he set out on a quest to discover what exactly the agency knew. In the process he uncovered a scandal that, though it has been little covered in the U.S., would rattle the Bundestag, blacken the BND, and deal the German media its biggest blow in nearly half a century.

Schmidt-Eenboom is a lanky man with a thick patch of whiskers and the quiet, determined air of someone on a mission. For more than a decade, that mission has been shedding light on the darkest secrets of the BND. He has courted leaks among the agency’s upper ranks and exposed hundreds of clandestine operations. In the process he created what one agency section chief called in an internal memo “a serious impairment to our future work.”

After the stranger’s visit in May 2005, Schmidt-Eenboom began scheming to retrieve his own BND dossier. He tracked down two agents who had spied on him and staked out their homes and private retreats, and they eventually spilled what they knew. Armed with this information he confronted the BND in July of that year, demanding it turn over his file. By September his request still hadn’t been answered, so he began threatening to talk to the press. Schmidt-Eenboom says that’s when he received an anonymous call vowing to “slaughter” him if he went public.

But he kept going. Schmidt-Eenboom knew the BND’s annual symposium was coming up on November 10. Shortly before, he began feeding information to Andreas Förster, a reporter for Berliner Zeitung. On November 7 the paper ran a story headlined “Taken In the Crosshairs,” which detailed how BND agents “hung at the heels” of their “favorite enemy,” Erich Schmidt-Eenboom.

Three days later, intelligence experts from Libya, Russia, and Japan poured into Berlin’s Hotel Estrel for the BND shindig. The topic du jour was nuclear proliferation, but the reporters who turned out only wanted to know why the BND would spy on journalists. Meanwhile, Schmidt-Eenboom kept feeding his colleagues exclusive scoops. “You have to wage a campaign,” he notes. “One story won’t do it.”

Mariah Blake writes for the United States Project, CJR's politics and policy desk. She is based in Washington, DC, and her work has appeared in The Atlantic, The New Republic, Foreign Policy, Salon, The Washington Monthly, and CJR, among other publications.