Ex-Wife Became My... Aunt?

The man the family has written off, the one kept in his rooms by a poison nobody has been able to treat, runs the most powerful spy network there is. Nobody in the house knows it, and the woman who marries him works it out only afterwards. She has been through this wedding once already. In her first life she married the man waiting at the front of the hall and gave him everything she had, and he took up with another woman, humiliated her and left her to die shut away in a cold palace while her whole family was put to death. She opens her eyes on her wedding day with all of it behind her and none of it yet done. She throws water in the groom's face in front of the guests, tears the marriage contract in half and says she is marrying the sick man in his family instead. The two of them make a deal. She will treat the poison with the medical knowledge she picked up in the life she already spent. In return he puts his people to work on the ones who ruined her. The marriage places her a generation above her former husband, who has to call her aunt now and serve her, and his mother has to bow to her as well.