Na-nan has known best pals Dong-mi and Jung-joon since childhood, and now the trio shares the ups and downs of their turbulent single lives together. But everything gets turned on end when Dong-mi and Jung-joon end up in bed! Should the longtime friends make it official or call it a mistake? Na-nan has a job offer and a marriage proposal from the charming Soo-heon to consider, and her twenties are fast coming to end.