Riko Rinda, known as the all-round appraiser Q, is a twenty-three-year-old woman with an extraordinary ability to determine the true nature and value of any object or situation. Her sharp observational skills, encyclopedic memory, and logical reasoning allow her to uncover truths hidden beneath layers of deception. She operates from her own appraisal shop in Tokyo, taking on clients who bring her puzzles that range from the mundane to the deeply mysterious.

Yuto Ogasawara is a reporter for a weekly magazine published by Kadokawa. He is assigned to investigate a strange phenomenon sweeping the city: stickers bearing the face of a sumo wrestler have been appearing on walls, signs, and public structures across Tokyo without any explanation. With his original appraiser abruptly quitting, Yuto turns to the internet and discovers Riko, the self-styled Appraiser Q. Reluctantly at first, she agrees to help him.

What begins as a seemingly trivial case of sticker graffiti quickly unravels into a series of much larger incidents. The investigation into the stickers leads the pair to an elaborate scheme involving counterfeit ten-thousand-yen notes that are flooding the market and threatening to trigger hyperinflation. Following the trail of the counterfeiters forces Riko and Yuto to travel to the remote island of Hateruma in Okinawa, where they uncover connections to Riko’s own past and the origins of her remarkable talents.

The story then shifts to a confrontation with a master forger named Karen Amemori, who specializes in creating flawless replicas of art, currency, and documents. Karen’s schemes force Riko to use her skills in increasingly creative ways. One arc sees Riko appointed as a temporary curator at the Louvre in preparation for the Mona Lisa’s exhibition in Japan, only to face a plot that threatens the painting itself. In another, she challenges the priest of a temple who claims his prayer boxes can grant any wish, revealing the mechanical and psychological tricks behind his deception.

Later, Riko and Yuto venture into a vast underground labyrinth beneath an ancient tomb in search of a legendary artifact said to have belonged to the onmyōji Abe no Seimei. The series also follows Riko as she goes undercover inside a publishing company suspected of tax evasion, posing as an internal auditor for the tax authorities.

Throughout all these cases, the manga maintains a tone of light-hearted intellectual curiosity. No one dies in these stories; the emphasis is on clever deductions, the joy of learning, and the gradual development of the partnership between Riko and Yuto. Their relationship, marked by Yuto’s earnest but sometimes clumsy support and Riko’s enigmatic confidence, provides a steady emotional anchor as they move from one puzzle to the next. The series adapts the light novels authored by Keisuke Matsuoka, illustrated by Chizu Kamikō under original character designs by Hiro Kiyohara.