At the once-a-decade jewelry cleaning festival at the Tsubaki Shrine, precious gems are purified by a special spring, enhancing their brilliance and value. During the event, taxi driver Ishikawa Genki notices two suspicious individuals secretly photographing license plates of luxury cars and alerts detective Kogoro Mori. Initially uninterested, Kogoro only springs into action when an attempted jewelry theft is reported.

The seemingly attacked woman, Matsuda Yoko, had voluntarily been the last at the spring and merely cleaned a diamond ring. Conan and Kogoro quickly suspect that her assault was staged to divert attention from a different scheme. While Ishikawa tries to help the woman, he is knocked out and locked inside his taxi.

It turns out the real target of the crime is a notebook containing information about wealthy participants and their jewels. The culprits, including Matsuda as an accomplice, plan further robberies using the stolen data. After a chase through Ginza, Conan and Ishikawa manage to corner the criminals and recover the stolen jewelry.

The episode ends with Ishikawa’s taxi, where the case was solved, as Mori and Conan fall asleep exhausted.