It was in Miami, last December, while sitting on a panel at an international book fair, that I tried to piece together the chain of events that had brought me to a place I knew I did not belong.

I considered the writers sitting next to me, three women who had written memoirs from places close to their hearts—stories of loss, family, selfhood. The questions from the audience, also mostly women, focused on each author’s emotional awakening and growth. How did we feel about the spiritual journeys we had undertaken? What lessons had we learned along the way?

I had no idea how I was supposed to answer, for a simple reason: My book wasn’t a memoir. As an investigative journalist, I had been researching and visiting North Korea for over a decade. In 2011, armed with a book contract, I went undercover to work as an ESL teacher at an evangelical university in Pyongyang. My 270 students—the elite of North Korea, the sons of high-level officials—were being groomed as the face of regime change to come under Kim Jong-un.

As a virtual prison state, North Korea is a place where the act of journalism is nearly impossible. Talking to citizens will get you nothing more than the party line, and most information about North Korea is related by Western journalists, who either visit the country on brief press junkets or record and repackage the unverifiable accounts of defectors. Having been born and raised in South Korea, I am fluent in the country’s language and culture, which enabled me to glean the subtleties beneath the surface, without the censoring presence of an official translator.

As I taught, I lived in a locked compound under complete surveillance: Every room was bugged, every class recorded. I scribbled down conversations as they happened and buried my notes in a lesson plan. I wrote at night, erasing the copy from my laptop each time I signed off, saving it to USB sticks that I carried on my body at all times. I backed up my research on an SD card, which I hid in the room in different spots, always with the light off, in case there were cameras. After six months, I returned home with 400 pages of notes and began writing.