Karen is reborn into a fantasy world as a noble, but she possesses no special powers, skills, or grand destiny. Her early life is comfortable until her mother inexplicably loses all memories of her. The revelation that Karen is the child of an affair follows, leading to her banishment from the family at fourteen to live as a commoner.

Two years later, her older half-sister becomes the sole concubine of the King of Falkrum. One of her demands restores Karen to the family, but the arrangement comes with a condition: Karen must choose a husband. Her options are Reinald Rodenwald, a dashing and mysterious second son of a marquis who has rejected all previous proposals, or the elderly, widowed margrave of the remote Conrad domain. Karen selects the margrave, reasoning he will die soon and leave her free to travel.

Upon arriving at the frontier, Karen discovers the margrave has a common-law wife and a son. Rather than a traditional wife, she is treated more like an unexpected daughter and potential heir. She receives a full education in running the territory and is respected as an adult, finding genuine happiness for the first time. Her plans for a quiet life are disrupted when she is called back to the capital, where she frequently encounters Reinald, who warns he will be a source of trouble for her. Reinald has dangerous secrets and connections, and though he saves Karen from a potential sexual assault, his true loyalties remain unclear.

The political situation in the Kingdom of Falkrum deteriorates. Karen finds herself caught in the consequences of decades of decisions, with war on the horizon. The first volume ends with a brutal attack on the Conrad domain. Bandits massacre the household, including the margrave's common-law wife and many servants. Karen barely escapes with the margrave's younger son and a few survivors. The King of Falkrum is assassinated, and in a matter of days, the nation falls under imperial rule. Reinald, revealing himself as a competitor for the imperial throne, seizes power ahead of his sister Wilhelmina.

Karen relocates to the imperial capital with the Conrad survivors to establish a new base. She becomes entangled in the power struggle between Reinald and Wilhelmina, with her own mysterious parentage becoming a subject of rumor. Speculation suggests her real father is a powerful military figure in the Empire, making her a valuable pawn. Karen is pulled deeper into imperial politics, even receiving an invitation to the Emperor's ball where failure to perform courtly dances properly could mean expulsion from the nobility.

The story introduces another reincarnated character, Ern, who is Karen's best friend. Unlike Karen, Ern uses her knowledge from her previous life to introduce modern weaponry to this world, starting an arms race with dangerous consequences. A major conflict emerges between Karen and Ern over this path, with Ern feeling like a fraud for merely copying things from their original world while desperately trying to make something of herself.

Throughout the narrative, Karen is an ordinary person navigating extraordinary circumstances. She possesses no special abilities beyond her wits and a modern perspective that makes her think differently than those born in this world. The series follows her struggle to survive as kingdoms fall, dynasties crumble, and she is pulled into a continent-wide power struggle she never wanted any part of.