S1E518 : Meiji Restoration Mystery Tour: Investigation

The Detective Boys are at a shrine dedicated to Shōin Yoshida, a famous figure of the Meiji Restoration. While there, they witness two men attempt to wrestle a book from a woman named Kimiko Kobayakawa. After the two men flee, Kobayakawa explains that the two men are after her grandpa's diary which contains the location of a treasure which could buy a country.