After Mako Oda's husband Kazuhiro's older brother, Masayuki, suffers a major setback at work and loses all his assets, he moves in with them as a permanent guest. Though hesitant at first, Mako agrees to her husband's suggestion to take him in. Meeting again after years apart since her divorce, Masayuki—fully aware she is now his younger brother's wife—finds himself overwhelmed by uncontrollable desire simply from sharing a roof with a woman. Mako struggles with her growing affair with her brother-in-law, tormented by guilt and fear of being discovered by Kazuhiro. Meanwhile, Kazuhiro remains calm and unchanged in his demeanor toward her, seemingly aware of her inner turmoil yet uncertain how to respond. A heartbreaking domestic drama unfolds, exploring the tensions between brotherly bonds, marital loyalty, and the painful consequences of infidelity.