The Governor of Tokyo, Yuuichiro Asakura, receives a threatening letter the day before the opening of Touto Line, a new train line for the Tokyo Metro. During the opening ceremony of the line, Conan Edogawa and the Detective Boys (Case Closed) are driven by Hiroshi Agasa (Case Closed) and pass under the Touto Line. Conan, having heard about the threatening letter, notices explosives connected to the Touto railway; Using his original voice to inform the police as Shinichi Kudo, he is able to stop the train and divert traffic away from the explosives preventing any deaths. Conan researches Asakura's political history for a clue on the culprit and learns the governor was in charge of the construction of dam in Kitanosawa, a fictional town in the Niigata Prefecture. Due to the dam's construction, the citizens of Kitanosawa were forced into a new town and their old homes were drowned by the dam. Since Asakura's trip to celebrate the anniversary of the dam is canceled by the bombing, Conan speculates information on the bomber could be found in Kitanosawa and plans a trip there.