Kogoro, Conan, and Ran are invited to dog food company president Anna's birthday party and arrive at the yacht harbor. Shortly after the party begins, Anna is shot to death by a masked man wielding a shotgun. Anna's ex-boyfriend Hyodo emerges as a suspect, but because he has an alibi, the police are unable to arrest him. The next morning, Hyodo's body is discovered alongside the shotgun that was used to kill him. Upon seeing the shotgun, vice president Inamura acknowledges that it belongs to him. Now that Hyodo has been murdered, the police believe someone else must be the true culprit, but Conan is certain Hyodo killed Anna...