The Crown Princess's Gambit

From the back cover

On the night before her wedding to the Crown Prince, a young noblewoman watches her father bring home the daughter he fathered with his mistress. She is, after all, her mother's killer—or so the family believes. When her mother died in grief after learning of her husband's affair with her own half-sister, Liana, the girl was left to raise her infant brother alone while her father celebrated with his other family.

On the seventh day of mourning, she visits Liana's villa and presents her aunt with a white jade hairpin—and a blade. Her father suppresses the murder to protect his name, but he poisons her food, intending to drive her mad within a month. She survives by throwing herself into a frozen lake, and her aunt, her mother's sister-in-law, takes her and her brother away.

To repay her aunt, she becomes companion to the difficult Princess Seraphina, enduring punishment with a smile while quietly learning the arts of governance. The Crown Prince notices her. But her father's hatred and her own secrets remain, and the game has only begun.