Yeon-joo (Kim Hye-soo) is a single mother with a bit of nerves. She is deeply troubled by bipolar disorder from time to time, and her daughter who has become overly sensitive during adolescence also gives Yeon-joo a headache. Due to some accidents, Yeon-joo's family encountered an unprecedented economic crisis. In order to subsidize the family, Yeon-joo had to rent out the room on the second floor of her house. That's how Yeon-joo met the man named Changren (Han Seok-kyu). Changren is a writer, but in Yeon-joo's eyes, he is just a wretched man with a suspicious face and strange whereabouts. During the days of living together, countless misunderstandings and jokes occurred between the two. Unexpectedly, it was these bumps that created a wonderful relationship between the irritable female landlord and the suspicious male guest, and the life of fighting and playing quickly brought the two closer.