The Devil's Power Couple

Serena Jenkins comes back to the Jenkins family as the daughter they once abandoned and lets them go on seeing her that way. She is also the doctor known as Satan, and nobody in the house knows it. Her stepmother and the stepmother's daughter are on the other side of the family fight, and Serena works her way into a position of authority without showing her hand. Then her father falls seriously ill. She tells the family who she is and sets the family fortune as her price for the operation. Her assistant has been beside her through this with no memory of his own past. When it returns he turns out to be Lucifer, head of a dark empire of his own, and the two of them have to settle whether they can trust each other before they can move together against the stepmother, take over the Jenkins family, and go after the secret organization that destroyed Serena's right hand years earlier.