The director of the zoo, Taketao Kawauchi, disappears mysteriously, and his daughter Sumiko asks private detective Homura Soroku for help. An investigation by Fancun found that the director was last seen in the reptile house and poultry greenhouse before his disappearance, and that the words and actions of Kamoda, the researcher at the reptile house, and Bei Wai, the director of the bait adjustment room, and others were suspicious. The three mysterious water tanks hidden in Kamita aroused Homura's suspicion. As the investigation deepens, various clues become intricate, and the director's pens, buttons and other items appear one after another, making the case even more confusing. What happened to the director? What secrets are hidden in the water tanks in the duck field? What's the conspiracy behind all this?
