It is adapted from Lee Se-in's 2007 novel of the same name about a furniture designer, Park Kae-in, who lives together with architect Jeon Jin-ho under the mistaken assumption that he's gay.

Furniture designer Park Kae-in (Son Ye-jin) is kind, impulsive, clumsy, and 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).

Despite being upset, Kae-in attends the wedding of her friend and roommate, serial monogamist 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.

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).

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.

The DAC director, Choi Do-bin (Ryu Seung-ryong), impressed by Jin-ho's presentation, offers his support to him in the upcoming project.