From 2007 to 2011 South Korean filmmaker and newspaper reporter Hark Joon Lee lived among North Korean defectors in China, filming an award-winning documentary on their struggles. "Crossing Heaven's Border" is the firsthand account of his experiences there, where he witnessed human trafficking, the smuggling of illicit drugs by North Korean soldiers, and a rare successful escape from North Korea by sea.

As Lee traces the often tragic lives of North Korean defectors who were willing to risk everything for their hopes, he journeys to Siberia in pursuit of hidden North Korean lumber mills;...