Ooka Momiji's Challenge (1)

Ran receives a message from Ooka Momiji. It is a request for Kudo Shinichi to solve a code. A housekeeper who worked for many years at the mansion of a wealthy man passed away, leaving her four sons a code. She loved mysteries and sent each brother a different code so they would have to work together in order to find the treasure. Immediately after the brothers shared their codes with each other, they lost contact with the eldest brother. Fearing he may have encountered trouble, they put out a request for the code to be solved and find their missing brother. Momiji is coming to Kyoto on this day in order to fill them in on the details, but...