"Happy Sisters" tells the story of sisters Yoon Ye-Eun (Shim Yi-Young) and Yoon Sang-Eun (Han Young).
Yoon Ye-Eun has been married for 7 years. She is a housewife and works hard taking care of the family on her husband's (Kang Seo-Joon) side. Her in-laws though give her a hard time, but she is positive and happy. Her husband's business is doing well and they move into a new house. Yoon Ye-Eun then finds out her husband is having an affair.
Yoon Sang-Eun is single and runs a small piano institute. While running her piano institute, she has fallen into debt. She meets Choi Jae-Woong (Oh Dae-Gyu) through a matchmaking agency. Choi Jae-Woong proposes to enter into a contract marriage with Yoon Sang-Eun and in return he will pay off her debts.
