Conan, Kogoro, Ran, and Sonoko are at a tea house when a woman wearing gothic lolita fashion clothing enters the tea house, orders a glass of water, and leaves. Ten minutes later, a woman named Yuika Shodo, arrives to the tea house where they learn that she was suppose to meet with the woman from before. The four then leave to go shopping. On the way, a pair of thieves tries to steal their shopping bags by spilling ice cream on Ran and Sonoko but are foiled by Conan. The girls are forced to change in a public restroom where they find the gothic girl from before dead.

The Detective Boys attend a firefly festival to commemorate a shinto shrine in a village. The truck soon arrives with the fireflies and they are released into the fields. Later one of the truck drivers, Tokuro Nakamine, is found murdered and three of the villagers are the prime suspects.