A young noblewoman is publicly accused of a crime she did not commit by her fiancé, the second prince, who then breaks off their engagement. As punishment for this false accusation, she is instead betrothed to Felix, a marquess known to be cursed. Following this abrupt reversal of fortune, the woman, Lucille, collapses and awakens with memories of her past eight lives. In each of those previous existences, she was not human but a beloved pet cat named Lilybell, owned by some of the most powerful figures in history, including a great witch, a legendary alchemist, and a chosen hero. She also recalls a prophetic vision that shows her future: she will be killed by a Saint who is destined to appear within a year.

Armed with the memories and instincts from her time as a cat and the skills she learned from her former owners, Lucille decides she will not passively accept this fate. She plans to simply enjoy her temporary engagement to the cursed marquess, believing his fated heroine will eventually arrive to cure him and take her place. The main setting is a fantasy noble society where magic exists and prophecies hold weight. Lucille’s new life begins in the household of Felix, whose curse isolates him from others and has made him a figure of fear and pity.

Lucille’s personality is heavily informed by her past as a cat; she is confident, unconcerned with social expectations, and prone to making poorly thought out but effective plans. She is oblivious to the romantic interest of Felix, who quickly becomes attached to her instead of any destined partner. As she settles into her temporary engagement, the story follows her using her inherited skills and positive attitude to help those around her, including her new friend Alice Rohans, who struggles with feelings of being ordinary in a family of geniuses.

A major narrative arc begins with the arrival of the heroine, Elvira. Believing the original course of events must be followed to cure Felix’s curse, Lucille attempts to push Elvira and Felix together. However, Felix only has eyes for Lucille. During this time, Lucille discovers that the legendary Great Sage, one of her former owners, is still alive but trapped in an unaging child’s body after making a deal with a devil. This same deal is the origin of Felix’s curse, and the Great Sage’s eventual death would break it. The plot moves toward this resolution as demonic forces threaten the domain.

The curse is ultimately broken by Lucille. With Felix freed, he is able to return to his family, confronting his mother’s guilt and misplaced anger over the curse. Elvira, having learned from her experiences, leaves for a holy country to improve her magical abilities after a philosophical argument with Lucille about saving the many versus the one. The main narrative concludes with Lucille still viewing Felix as a friend rather than a romantic partner, having successfully averted her prophesied death and unraveled the mystery behind the curse.