After his mother's death, 16-year-old Hyung-ju suspects that his father is not his biological father. A secret paternity test reveals that he is not. Confused, he uses his math skills to figure out his biological father and embarks on a journey with his best friend, Ji-su, to find him.

After completing his required decade of military service and being honored as a hero, a North Korean sergeant makes a sudden shocking attempt to defect to the South, risking life and limb for the chance to finally determine his own destiny.