Furniture designer Park Kae-in (Son Ye-jin) is kind, impulsive, clumsy, and is a complete slob in her personal habits. She lives in Sanggojae (meaning "a place for mutual love"), a modernized hanok (traditional Korean house) designed by her father, a famous and reclusive architecture professor (Kang Shin-il). As an independent furniture designer, she struggles to produce successful products and is constantly trying to impress her father with her works. Her long-time boyfriend, Han Chang-ryul (Kim Ji-seok), breaks up with her, the reason being Kae-in is an easy woman and a pushover. Despite being upset, Kae-in attends the wedding of her friend and roommate, Kim In-hee (Wang Ji-hye), only to discover that she is marrying Chang-ryul; and that the two had been seeing each other behind her back for a while. After she finally comes face-to-face with them, the wedding ceremony turns chaotic and is cancelled. Kae-in is heartbroken and determined to never take a chance on love again.
Meanwhile, to keep his small firm afloat, architect Jeon Jin-ho (Lee Min-ho) is desperately trying to win a project bid for the Dam Art Center against Future Construction, the company owned and operated by Chang-ryul's father (Ahn Suk-hwan). Chang-ryul's father was originally an employee under Jin-ho's father, who stole the latter's company. In order to win the project of Dam Arts Center, Jin-ho has to find a way to dig up more information about the tentative theme of project: Sanggojae, which has never been opened to the public.
Jin-ho decides to rent a part of Sanggojae to get access into the house while Kae-in rents the place to him believing that he is homosexual due to misunderstandings from their previous encounters. After knowing the reason behind his approval, Jin-ho decides to leave Sanggojae to avoid being misunderstood further but is stopped by his assistant, Noh Sang-jun, who convinces him otherwise by reminding him that their chance at revival of their sinking firm lies on their success in Dam Arts Center Project.
After starting to live together, Jin-ho tells Kae-in that she's miserable only because of herself and the lack of concreteness in her personality. He then encourages and helps her transform from an inveterate slob into a better version of herself, who is confident and strong-willed. Amidst the transformation and hidden truths, Kae-in and Jin-ho start developing feelings for each other which they constantly deny.
The DAC director, Choi Do-bin (Ryu Seung-ryong), impressed by Jin-ho's presentation, offers his support to him in the upcoming project. He also finds Kae-in's ideas creative and hires her to design a recreation centre for children. Do-bin, who is homosexual, later finds himself attracted to Jin-ho, which leaves Jin-ho in a tight spot.
What will happen when the man who's pretending to be gay and the woman who thinks he's gay develop feelings for each other?
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