A drama about the careers and love lives of urban professionals. It will tell the story of four men in their forties as they go through love, breakup, success and failure. Kim Do-jin, an architect with a scathing tongue have romantic relationship with strict high school teacher Seo Yi-soo, who moonlights as an umpire at amateur baseball games. Im Tae-san is dating a cold-hearted woman but wonders if there is someone else out there for him. Choi Yoon tries to heal his heart after losing his wife seven years ago. Lee Jung-rok marries an older woman for money but may lose his comfortable lifestyle in a divorce.
Seo Yi Soo and Kim Do Jin keep meeting each other in the least expected ways and places. Do Jin deduces Yi Soo is in love with Tae San, a mutual friend.
Because of Me Ah Ri's, Tae San's younger sister, meddling, Yi Soo is forced to make a false declaration of love to Do Jin in front of Tae San.
After Yi Soo makes the false declaration of love to Do Jin, she ignores his calls and messages. Do Jin declares that he will have one-sided love towards Yi Soo.
Jung Rok swallows his wedding ring. Yoon accidentally lets Do Jin know he likes Mae Ri. Se Ra, after seeing Tae San's yearbook photo on Yi Soo's possession, realized the man Yi Soo likes is Tae San.
Se Ra catches wind of Yi Soo's feelings for Tae San and tries to get her to admit it.
Because of her jealousy, Se Ra reveals to Tae San who is Yi Soo's unknown crush. Do Jin kisses Yi Soo.
Tae San tells Yi Soo he likes Se Ra a lot. Se Ra tells Yi Soo she knows she likes Tae San. Yi Soo tells Do Jin she will start dating younger guys. Yoon is jealous because he keeps seeing Maeahri with Colin.
Me Ah Ri publicly confesses her feelings for Yoon, putting Tae San and Yoon in an awkward position.
Yi Soo wears the pink shoes given to her by Do Jin. He's happy when he sees her wearing them until he hears what he thinks it's her second false declaration of love, which hurts and upsets him. Because of this, he doesn't want to see her again. Once Yi Soo is back home, as the bubbles in her fantasy break like glass, she realizes she has fallen for Do Jin.
In an unexpected twist of events, Yi Soo is chasing after Do Jin in order for him to accept her apology.
Do Jin creates a "one-sided love" checklist for Yi Soo to complete so that they're even.
Tae San and Se Ra get into their biggest fight yet, which might mean the end of their relationship for good.
The guys decide they can't ignore Colin anymore and set out to send him back to Japan.
Everyone is curious as to who Colin's biological father is, creating a mess of misunderstandings and accusations between the guys and their significant others.
Jung Rok, Yoon and Tae San are all determined to be good uncles to Colin while unknowingly embarrassing him in the process.
Yi Soo struggles to come to terms with Do Jin's situation; meanwhile she becomes Colin's new homeroom teacher.
Yi Soo puts all her faith into Do Jin returning to her, one last time.
Yoon finally removes his ring, admitting his feelings for Mae Ahri. Angry, Tae San disowns them both, prompting their friends to comfort and cheer them on separately. Min Sook’s mistrust of Jung Rok will never fade so she sincerely asks for a divorce while Mae Ahri and Yoon officially embark on their first date. Do Jin charms Yi Soo’s fellow teachers by treating them to dinner, ending the night awkwardly listening to provocative music as their feelings for each other continue to grow.
So Tae San finally agrees for Yoon and Meari to be together, but with the condition that they must get married. Meahri and Yoon agree with Tae San to get married. Meanwhile Rok and Min Sook file their divorce. Min Sook now single decides to throw a bacheloratte party for Meahri and the the F44 end up crashing the party.
Yoon and Meari's wedding. Jungrok try to win Minsook back. Dojin’s proposal to Yisoo. Sera fainted because she's pregnant but will not get married until she delivered the baby.