Hui Won, an ER nurse, transfuses her own blood to save Tae Yeong, 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 Yeong hands her a contract: be his fake wife for one year. With 3 billion won and her father's medical bills on the line, Hui 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.