A connection is found between a string of arsons and a 12 year old murder.

Kisou 235 II

Kosuge, the president of a factory, is killed by someone while returning home. A bag charm is found at the scene. When Akira Higuchi and his colleagues from the Metropolitan Police Department's Investigation Division investigate his home, they find a bankbook with the letters A, Y, M, and S written in English. It turns out that the charms left behind were custom-made by Seiji Iwai. However, Seiji had committed suicide five years ago in a robbery-suicide case. Seiji's mother, Mizuki, is an old acquaintance of Superintendent Tendo. Higuchi heads for Mizuki's place...