Why are immortal vampires being killed? "Birdcage Messenger" - that's the detective who specializes in investigating monster cases. Vampires and androids, phantom thieves, werewolves, rippers, and famous detectives. In late 19th century Europe, where aliens were stirring, human-friendly vampires were pierced to death by silver stakes. The detectives who came to solve the case were Rindou Yaya, who specializes in "monster cases" that humans avoid, and Shinu Tsugaru, a man with a strange birdcage. They derived inferences from the remaining clues and the characteristics that only monsters have. A comedy full of mysteries and like a nightmare begins here!