Na Kyung-soo, a diver, is angered to learn that the Coast Guard is assigning responsibility for the death of a fellow diver during the Sewol ferry disaster recovery to Ryu Chang-dae, the representative of civilian divers, and charging him with manslaughter.

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.