So-jin, a DNA researcher, gets dumped by his boyfriend, Sang-min. Heartbroken, she drinks too much and breaks into a stranger's house. Yeon-woo, a successful gynaecologist, breaks up with his girlfriend as he gets sick of her. Kang-hoon, a hardworking firefighter, finds a pregnant woman unconscious. Meanwhile, So-jin witnesses Sang-min walking down the street with a woman she knows.

So-jin discovers that Yeon-woo has a special scent that she's attracted to, so she decides to figure out if he's her DNA lover. So-jin meets her sister and mother to commemorate her dad's death anniversary at Kang-hoon's restaurant. The family gathering doesn't go too well, and they end up fighting. Yeon-woo, who happens to be at the restaurant, overhears So-jin's family's history.