Han Eok-kwan (Cho Jae-hyun) is a ruthless, foul-mouthed small-time gangster in Busan. When fellow gangster Dok-sa (Lee Jae-yong) betrays their boss Byun Hak-soo (Im Dong-jin) to take his place as the new boss, Eok-kwan is exiled from the gang. Then a former lover contacts him to meet her in Seoul, but once he gets there, all he finds is a 10-year-old boy named Jae-soo, who claims to be his son. At first he plans to abandon the boy, but unable to do it, ends up raising him.
Shin Hye-rim (Jo Min-su) is a widow with two children, 12-year-old daughter Soo-ah and 10-year-old son Kyung-ho. After her husband, a district attorney, dies, she leaves Seoul with her children and moves to Busan, where she opens a piano school. Eok-kwan falls head over heels in love with the piano teacher, and they later marry.
Shortly after, Hye-rim dies in a boating accident. Soo-ah and Kyung-ho, who've always resented their new stepfather, blame him for her death and try to leave the family home, but Eok-kwan begs them to stay. Transformed into a loving and hardworking father, he raises the three children to the best of his abilities.