Conan, Kogoro, Amuro, and Irohazushi chef Wakita take the Azusa limited express to Nagano. Originally, Sonoko was supposed to go with them, but she fell ill. Since Ran stayed behind to visit her friend, Amuro and Wakita took their places on the trip because the client Nichihara Taisei insisted in his letter to Kogoro that he bring a group of four. Included with the letter was a code written in katakana. The client's request is, "My old friend hanged himself in an abandoned church deep in the mountains of Nagano, and I have no idea why. Please decipher the code and tell me the truth." In the chapel of the abandoned church they arrive at, they find five of Nichihara's former high school classmates...