In a quiet corner of Kamakura, a small used bookstore named Biblia Koshodō is the setting for a series of literary mysteries. The owner, Shioriko Shinokawa, is a strikingly beautiful young woman whose extreme shyness makes everyday conversation a struggle. When the topic turns to antiquarian books, however, her passion overcomes her timidity and she becomes an eloquent and incisive storyteller. Her deep knowledge of old books is matched only by her sharp observational skills, and she possesses a rare ability to unravel the secrets that each volume carries.

The story begins when Daisuke Gōra, a young man who grew up with a phobia of reading, brings in a set of his late grandmother's books for appraisal: the complete works of Natsume Sōseki, each volume bearing what appears to be the author's signature. Daisuke had once glimpsed Shioriko in high school and been struck by her presence, and their chance reunion at the bookshop sets their relationship in motion. Drawn into the shop's orbit, Daisuke becomes a part-time assistant, and together they encounter a steady stream of peculiar guests, each carrying an old book that hides a personal mystery, a forgotten history, or a delicate secret.

The manga weaves together standalone episodes and longer narrative arcs. Early cases involve a signed Sōseki collection with a hidden message, a missing volume of poetry that connects to a family rift, and a rare edition of a children's book that holds a clue to a decades-old disappearance. Over time, the mysteries grow more personal. Shioriko reveals that she was injured not in a fall but was pushed, and the investigation into who attacked her and why becomes a central thread. Daisuke's own background comes into focus as his grandmother's books and their connection to Shioriko's family are explored. The relationship between the shy, book-obsessed shopkeeper and the gruff, non-reading assistant deepens gradually, anchored by their shared curiosity and growing trust.

The series is distinguished by its focus on real, often obscure, antiquarian books. Each title featured in the story is an actual published work, and the plots draw on the physical and historical details of these books: marginalia, inscriptions, publication quirks, and provenance. The setting in Kamakura, with its temples, quiet streets, and seaside atmosphere, provides a gentle backdrop that complements the intellectual and emotional tone of the narratives. The manga adaptation closely follows the original light novel series, covering the early volumes and the main storyline involving Shioriko and Daisuke, with later manga installments continuing into the second generation of characters.