Mouri, and Conan are checking out costumes for Mouri's one day of being a chief firemen. Later they meet people attending a costume party. While walking home, they find a police car in front of the house and meet the people from the costume shop earlier, realizing the host has been murdered. Conan realizes that the culprit must've interfered with the Rigor Mortis and finds the evidence to convict the culprit. The culprit reveals that the host was his controlling girlfriend.