When Geumseong's phone rang on Christmas Eve 2020, he answered nervously. The previous year he'd made the perilous journey to escape from North to South Korea, using an international underground network of safe houses and brokers. Eventually his mother's voice came from the speaker: "Geumseong, Geumseong, can you see me?" Eunhee could hardly get her words out through sobs as her teenage son clasped his hand to his mouth. "Mum, I'm doing well and I'm not sick," Geumseong quickly reassured her. The relief at seeing his mother's face was overwhelming. "So much time has passed," she replied. "I can hardly recognise you." Geumseong proudly announced he was now taller than his mother. He lifted his hair, showing his teenage acne to make her laugh. Then he picked up the phone and took her on a tour around his new home in the South Korean capital, Seoul. "The house has three floors, it's really big!" exclaimed Geumseong. "It even has a piano." "Wow!" his mum responded.…