North Korea is the only place in the twenty-first century where there is no freedom of movement. However, there are people who have crossed the border into the South, as in this book. 
The protagonist, Juyeong, starts working at UNIWON, a resettlement education organization that helps North Korean defectors. There, Juyeong meets North Korean children who have defected to the South for various reasons. The novel talks about concerns and hardships of North Korean defectors living in South Korea.