As Mori, Ran, and Conan are on their way home from a hot spring, they boarded a train together with a pair of doctors. They arrived at a station where one may change trains to another line, but no one could possibly change trains since the two lines are scheduled differently by a mere five-minute difference. At the station where the trio are to change trains to one going to Tokyo, a murder is discovered. The only suspect rides in the train with Conan's group while the victim rides on a train from a different line. Conan uncovers the trick used by the murderer using the change given by a lady working on the train of the victim.