It was still dark outside when the sound of murmuring engines and fishermen testing marine radios awakened the small harbor of Daejin on South Korea’s east coast. Park Cheol-hoon and his father loaded their three-meter-long boat, the Cheongjinho, with nets and spears, then set out to catch seafood for their family restaurant. Their destination: waters perilously close to North Korea, the place they fled 18 years before.