Jeong-woo, who is newly married with Na-yeong, is secretly meeting Na-yeong's close sibling, Min-joo. Na-yeong, who is not aware of that fact, is worried that she is alone and tells him that he will introduce a good man to him, but she disappears when she tells him that she does not need a man and tells her not to do unnecessary things. Meanwhile, Na-yeong, who came home, tells this to her husband, Jeong-woo, but Jeong-woo also shows a grim reaction and does not care about it. Then one day, Min-joo visits Na-yeong's newlyweds in surprise, and the three of them fall asleep while drinking happily. While sleeping, Min-joo comes to Jeong-woo and does something amazing. A fierce love between a close brother and the man of his sister is just beginning.
Na-hee spends a day with alcohol after parting with her lover, Ji-hoon. Min-yeong knows and tries to take care of Na-hee. However, Na-hee does not forget Ji-hoon, and in fact, Ji-hoon and Min-yeong, who was former partner, have a relationship with Ji-hoon, who came to Na-hee. Na-hee, who is not aware of this fact, contacts Ji-hoon again, asking for forgiveness.
Na-yeong and Min-hyeok become lovers and have a relationship, but they live together on the premise of marriage. At their first housewarming, the two invite their friend Jin-woo. Jin-woo, who is invited, keeps telling bad stories to Min-hyeok, and Min-hyeok, who is only gentle, thinks it is just a joke. Meanwhile, Na-yeong who is angry at Jin-woo's appearance, talks with Jin-woo about Min-hyeok, who is asleep. However, there was a hidden past between Jin-woo and Na-yeong. In fact, the two were sex partners.
