If you were to meet me again in another world, would it be a coincidence? Or is it fate? I hope it is destiny.... Cha Shin-hye, who must enter into a political marriage as her father wishes. It was a contract she chose because she hated the life of having to follow in her father's footsteps in politics, but she is not happy. In her lethargic daily life, one day she dreams of a red string symbolizing 'fate' and meets someone who completely shakes her heart. Feeling a strong thrill and captivated by Ain's presence, Shin-hye becomes confused and is convinced that she is the 'red string' of her fate. Eventually, they realize their feelings are mutual and fall in love. The relationship with Ain, which she believed would be purely happy. However, as time goes by, Shin-hye feels a strange sense of disconnection from Ain and struggles. Moreover, her workplace colleague and mentor, Team Leader Lee Ji-an, keeps lingering in her mind. As time flows in a relationship where it's hard to tell who is fate and who is misfortune... Who will Shin-hye choose? And who are her red string and black string?