Ahmadinejad was in New York for the 65th United Nations General Assembly—or UNGA, typically pronounced just the way it looks. While the Iranian leader’s visit was particularly high-profile and politically fraught, it was by no means unique. In 2010, the annual event required more than 200 Secret Service details for foreign leaders, American officials, and spouses, along with another 60 or so State Department security details for lower-level protectees. (This is in addition to the thousands of New York City police officers called upon to help secure buildings and traffic routes, and lead motorcades.) Over the course of the event, 900 aircraft would fly in and out of JFK bearing dignitaries; hundreds of events across the city would need to be scouted and secured.

Yet, remarkably, the General Assembly has become an almost unremarkable event, at least by Secret Service standards. There have been 38 “National Special Security Events” since President Clinton first coined the term in a classified 1998 national-security directive. Most of these NSSEs have occurred since September 11, 2001, and 14 of them since 2007, including the two presidential conventions, President-elect Obama’s pre-inauguration whistle-stop train tour, the inauguration itself, and the 2008 and 2009 G-20 summits. The General Assembly poses greater security and logistical challenges than many, if not most, of these events. This is due in part to its size, and in part to the fact that habit is the worst enemy of protective security, and the assembly offers an extremely attractive, recurring target: many foreign leaders stay in the same hotels and attend the same events at the same times each year. But despite all this, the General Assembly has not been categorized as an NSSE since 2001. The Secret Service has it down to a science.

This is the story of a dog that didn’t bark, and of the men and women who kept it muzzled. The Secret Service receives dozens of requests each year from reporters who want a peek inside the agency; most are quickly turned down. Typically, the service provides context for media coverage of its major security events by opening its training facility in Beltsville, Maryland. There, it can put on a show—complete with motorcades and simulated attacks—in a tightly controlled environment. It took me more than 18 months to persuade the service to let me be the first reporter to see the process from the inside in a real-world, real-time situation. I was allowed access to command posts, operation centers, and other secure areas. I agreed only to withhold some details about protective methodology that would imperil the service’s ability to do its job.

In exchange, I was able to witness how a smallish, secretive federal agency under some bureaucratic duress assures security at the General Assembly, an event for which two-thirds of the world’s leaders, many of whom have been subject to past assassination attempts, gather in one of the most crowded, open cities in the world. It is the job of the Secret Service, in concert with a host of local, state, and federal agencies, to make sure nothing goes wrong.