Lumina Raymond, the daughter of a fallen noble house, is ready to throw away her happiness to save her family. With her older brother bedridden and her estate in shambles, she agrees to a desperate engagement with Marquis Lugol Carious.

But her life is upended when a letter arrives from her future self, written one year in the future. The message is a warning, her brother will die, and her life will end in total ruin. According to the letter, there is only one path to salvation—she must choose the man she once turned down, the "Cold-Blooded Duke," Lian Leidlant.

With her future on the line, Lumina marches right up to the notorious "Cold-Blooded Duke" to say the words that will change everything:

"I choose to marry you after all!"