The novel follows Richard Ranashinha Dvorpian, a handsome British jewelry appraiser, and Seigi Nakata, a bright and upright Japanese college student. The duo solves various jewel-related cases by unraveling the hidden .

Possessing a deep knowledge of mineralogy, Richard Ranashinha de Vulpian is a young and handsome British jewelry appraiser who owns a small shop in Japan. One fateful night, Seigi Nakata, a righteous college student, saves him from drunks who were harassing him due to his good looks. Upon learning of Richard's identity, Seigi hires him to appraise a pink sapphire ring that was left behind by his deceased grandmother. Before long, Seigi becomes a trusted part-timer at Richard's shop. Together, the duo solve various jewel-related requests from diverse clients of different backgrounds. Step by step, they unravel the hidden motives and feelings that lie within the gems in order to understand and empathize with the little stories behind each piece of jewelry.—MAL Rewrite

One night, a college student with a strong sense of justice, Seigi Nakata, saved a gorgeous foreigner, Richard, who was being harassed by some drunks. When Seigi found out that Richard was a jeweler, he asked for an appraisal on a ring with a shady history; one which his grandmother had kept secret until she died. The appraisal had revealed her past, truth, and desire. It led Seigi to work as a part-time employee for Richard's jewelry store, the "Jewelry Etranger" in Ginza. While solving various "mysteries", the relationship between Richard and Seigi gradually changes.—Crunchyroll