Hee-won, an ER nurse, transfuses her own blood to save Tae-young, a mob boss who arrives with a gunshot wound — only to discover his deadly secret: hemophilia. On the day of her wedding, her fiancé's betrayal leaves her with nothing. Tae-young hands her a contract: be his fake wife for one year. With 3 billion won and her father's medical bills on the line, Hee-won is locked away in his mansion. She pushes back against his cold obsession and control, but slowly uncovers the loneliness and warmth hidden beneath his ruthless exterior — and the more she tries to escape, the deeper she falls.