Clarice, the eldest daughter of the once-noble Ducale family, faces ruin. Her father is buried in debt, and her younger sister Charlotte is gravely ill, requiring expensive treatment the family cannot afford. Desperate to save her sister, Clarice agrees to an arranged marriage with the Dark Knight, a notoriously powerful, wealthy, and terrifying warrior who never removes their magical black armor. She plans to seduce her new spouse and use their fortune to rescue her family.

On the wedding night, Clarice discovers a shocking secret: the Dark Knight is a woman named Frost Von Galleria. In a kingdom where female knights are forbidden, Frost threatens to kill Clarice to protect her secret. Undeterred and with her life now on the line, Clarice shifts her objective from simple seduction to a more complex challenge: she must make Frost fall in love with her. This would not only secure her own safety but also ensure financial support for her sister.

The story is set in a dark fantasy world populated by monsters, where a rigid patriarchy dictates that women cannot serve as knights. The narrative quickly moves past the wedding to focus on Clarice’s attempts to navigate her new, dangerous household. The residence is filled with servants terrified of the imposing master, while Frost herself is socially awkward and isolated, unsure how to interact with her new wife. Clarice uses her intelligence, cooking skills, and determination to bridge this gap, attempting to break down Frost’s emotional walls.

A notable initial arc follows Clarice’s efforts to woo her reluctant spouse. She challenges Frost to activities like chess, only to find that no one has ever dared to play with the fearsome knight. At the same time, Clarice must manage the household staff and contend with sudden monster attacks that demonstrate Frost's formidable combat abilities. The comedic tension comes from her sister Charlotte at home, who daydreams harmless fantasies about her new brother-in-law, unaware of the dangerous and romantic turmoil Clarice is actually facing. As Clarice works to erase the Dark Knight’s frightening public image and earn Frost's trust, genuine feelings begin to develop, though the looming threat of Frost’s secret being exposed puts both their lives and their budding relationship in jeopardy.