The Detective Boys run into a strange man named Kyozo Daita who invites them to a cake shop after stopping a thief for him. While talking with him, Conan notices the man is acting strangely. The next day, Kogoro receives an anonymous request to investigate a case involving red shirts with long sleeves. The mysterious caller requests to meet them on the third floor of a department store. At the store, the three then run into a man who explains he has been strapped with bombs. The man explains he was knocked unconscious in the bathroom and found himself like that. He explains the bomber told him that if anyone leaves the floor or calls the police, the bomber will detonate the bombs in the building. He discloses the bomber's demands, to find the sender of thirteen red shirts.