Big Gold Bullion - Boy Detectives Club, #4

During the last days of the Shogunate, the paranoid patriarch of the Miyase clan, once one of the five wealthiest men in old Edo, sold all of his possessions, bought a hoard of precious metals, and buried the stash somewhere beyond the borders of Tokyo. The hidden location of what came to be known in family lore as the "Big Gold Bullion" was ultimately entrusted to Fujio Miyase's equally eccentric uncle.
But succumbing to a sudden illness, the only clue he left behind was a secret message with no decryption key. Now it is up to Detective Kogoro Akechi and Yoshio Kobayashi, his able young assistant, to crack the code and recover the treasure before small army of cutthroat villains gets there first. They are going to have a fight worth literally millions on their hands.