Yeonsu, who had been supporting her family alone after losing her father and caring for her ailing mother, one day receives a shocking proposal from Madam Son, the wife of Assemblyman Yoon, her late father’s longtime friend. The proposal? To bear the child of Cha Taegun, executive director of Haeshin Group, in place of Madam Son’s own daughter, Hyein. Yeonsu adamantly refuses, but with her sick mother used as leverage, she is left with no choice but to accept. “You signed the contract with your own hand. You agreed to bear my child.” As Taegun holds Yeonsu, he expresses his turbulent emotions through rage and contempt, and the more time Yeonsu spends in his bed, the more confused her heart becomes. As time passes, the complicated emotions between the two begin to stir... eventually setting off a rising wave of blue.