The 11th popular series in which Kyosuke Kamizu, a university professor and a famous detective, challenges the mystery of the murder case. A bank clerk Fukushima was killed by a cyanide compound on a crowded train. Newspaper reporter Yamashita and colleague Kaori, who were on board, immediately started interviewing. In addition, Kaori asked Kyosuke Kozu (Masaomi Kondo), a university professor who had previously elucidated the murder of prussic acid by tablets, for cooperation. As a result of the investigation, it is discovered that Fukushima, who was killed, violently attacked a female college student with his colleagues and forced him to commit suicide...

Miyoko and Yusuke love each other. But Yusuke is told to work in Hokkaido where is far from Tokyo for a year. They cannot meet often. There appear another woman and man in front of each of them. They almost lose confidence to keep their relationship but finally they make sure of their love.