The FL gets reincarnated in a novel she once read as the daughter of the Marquis Morgana, a woman who gets pressured into marriage without love and who'll get abandoned by her husband after he cheated on her with her maid. To change her fate the FL had changed the position of her family compared to the book, but this has already happened where the book starts, so we can skip to the interesting part:

There is a magic contract between two families, a powerful grand dukedom Kallakis and family of marquis Morgana, that their descendants have to marry one day. That's what the adoptive son of the grand Duke wants to use to pressure the FM into marriage without love, because if not fulfilled the contract will have serious consequences.

But the FM knows that would happen if she were to marry the adoptive son, so she demands to marry not him, but his bachelor of a father. The adoptive son, doesn't cooperate and acts very foolishly, which caught the attention if the grand duke, who lived isolated from novel society.

At the end of chapter 4 the grand duke decides to go to the Capital, where the FL waits for her future husband