Born without magic in a world where gem appraisal depends on it, Audrey Evans is a noble lady in name only. She works as the lowest-ranked clerk at the Carpasi Magic Gemstone Company, a black-market-like merchant house that treats her as a disposable errand runner. Her father, a renowned A-rank appraiser, has died. Her fiancé, the company president Zoltan Carpasi, sees her as worthless and coldly breaks off their engagement. On the verge of despair, Audrey encounters Crista, a whimsical and powerful quartz spirit. Out of circumstance, Crista enters a magical pact with Audrey, granting her the mana she has always lacked. The spirit's power turns out to be overwhelming, giving Audrey not only the ability to appraise magical gems but also access to devastating spirit magic.

Audrey quits the company, opens her own Evans Appraisal Office, and sets out to live life on her own terms. Her first client is Lex Harrison, a brooding young magic tool craftsman who works with magical gems. Through him, she learns more about her father's hidden wishes and deepens her resolve. Her skills attract the attention of Miranda Harrison, Lex's grandmother and a former countess who is a passionate collector of magical artifacts. As Audrey's reputation grows, her former tormentors, the showy high-rank appraiser Dorr Birkin and the scheming Zoltan, begin to suffer from their own declining credibility. Their jealousy escalates into a direct challenge against Audrey.

The story unfolds in a fantasy kingdom where magical gems are used for everything from everyday tools to luxury goods. Spirits tied to specific crystals can form contracts with humans, granting extraordinary abilities in exchange for some form of compensation. Audrey's journey takes her from the grimy back room of a gem shop to high-difficulty excavation sites in search of rare gems like the Desert Rose, and later into open confrontation with the corrupt power structure she left behind. Along the way, she also forms a tentative bond with Black, the spirit of the Heavenly Black Opal, who was once an enemy but eventually becomes a housemate, revealing a surprisingly caring nature. Princess Rosearia of Lapis, a third princess known for her unconventional and charitable approach to trade, also takes note of Audrey's talents. The series balances Audrey's genuine love for gems and her quiet determination to live freely with escalating conflicts that test her newfound abilities and her principles.