Seigi Nakata finds a pink sapphire ring in his grandmother’s house and is warned by her to never do bad things. Years later Seigi saves jewel appraiser Richard Ranasinghe de Vulpian from drunks. With his grandmother dead Seigi hires Richard to appraise the ring. Seigi prevents university classmate Shoko Tanimoto being tricked by a pervert and develops a crush on her. Richard warns Seigi the ring is stolen, although Seigi already knew this. He explains his grandmother had been an unemployed single mother and was forced to steal to support her daughter Hiromi, Seigi’s mother, and stole the ring from a woman who later attempted suicide. Seigi’s grandmother kept the ring to punish herself while Hiromi grew to resent her. Seigi asks Richard to find the original owner so his grandmother can rest in peace. Coincidentally, Richard already knows the owner, Miyashita Tae, who explains it was her engagement ring, but the marriage was purely a business arrangement. When the ring was stolen she was relieved and ended the engagement but was rejected by her family, so she attempted suicide, ended up in hospital and met the doctor who became her husband. Rather than blame her Miyashita is grateful to Seigi’s grandmother and tells him to keep the ring. On Richards advice Seigi finally speaks to his mother about his grandmother and learns she helped name him Seigi, meaning Justice. Richard, convinced Seigi is honest and trustworthy, hires him to work part-time at Jewelry Etranger.

New customer Akashi Mami asks Richard to appraise her ruby brooch to see if it has been heat-treated. Seigi comments on the unusually bright colour, which Richard identifies as “Pigeon blood” meaning it was mined in Myanmar and is thus much more valuable. Richard is suspicious of Akashi’s interest in heat-treating as that only concerns the stone's monetary value. Seigi learns from Shoko, who has studied mineralogy, that heat-treating makes rubies 10 times more valuable. Richard is accosted by Homura Takashi, Akashi’s fiance, who believes she is having an affair with Richard. After the mistake is cleared up Homura reveals Akashi is actually called Sasu, and she has recently become miserable. Sasu arrives to collect her brooch but when she sees Homura she gets upset and breaks up with him before fleeing. Seigi follows and she reveals that she is actually a lesbian and had a relationship with a woman named Akashi Tatsuki for 7 years. She only agreed to marry Homura because her family expected it, but the stress of living a lie has made her sick, and she faints. After Homura learns the truth at the hospital he accepts the end of their relationship. Sasu later returns to collect the brooch, which Richard values at 10 million yen, and she decides to return it to Homura while living her life as she wishes.

Shoko invites Seigi to a mineral show and asks for his number. A young boy, Hajime, brings a gem to the shop Richard identifies as a Chrysoberyl Cat's Eye, and asks to purchase a second one. Richard fetches several made from Apatite and Tourmaline and explains how cat’s eyes contain Rutile, which creates the pattern. Hajime rejects them for being the wrong colour. Seigi determines Hajime wants them to represent a real cat. Hajime admits he adopted a stray cat named Milk, who saved their lives by predicting future events, but his father inexplicably got rid of him. Hajime’s mother is in hospital with pregnancy complications and his father gave him the cat’s eye to replace Milk’s protection, causing Hajime to seek out another for his mother. Seigi suggests Hajime’s father may not realise how upset Hajime is. Hajime’s father Yasaka arrives, Richard having called him as Yasaka had purchased the first cat’s eye from Richard. Yasaka finally explains that Milk had a parasite called Toxoplasma which is dangerous to pregnant women, so he gave Milk to his secretary, planning to retrieve him after the baby was born. Richard explains that Hajime’s gem is known as a “Honey and Milk” and Yasaka selected it especially for Hajime. Yasaka promises not to keep secrets from Hajime again and they leave satisfied. Seigi is impressed with Richard’s recall of previous customers but is shocked to learn Hajime’s gem is worth 10 million yen.