Bemu (Kazuya Kamenashi) , Bella (Anne Watanabe) and Bello (Fuku Suzuki) are humanoid monsters. Normally they live like a family and have the appearance of humans, but when they get angry or sad they change into ugly monsters. Due to their sense of justice they also help humans, but humans are fearful of them. Bemu, Bella and Bello have been living like this for several hundred years. Their wish is to become humans as soon as possible.

One evening, Bemu meets Detective Natsume (Kazuki Kitamura) by helping another man. Bemu is invited to eat with Detective Natsume's family. At the home of Detective Natsume, Bemu happens to see a picture. In the picture there is an individual who may hold the clues of becoming a human. Bemu, Bella and Bello meet the person in the picture, Professor Ogata (Morio Agata). Ogata claims he does not know anything about that. Bemu, Bera and Bero are disappointed. Soon, Professor Ogata disappears and Detective Natsume finds himself in the middle of a mysterious case.