The Mystery of the Otter is the first book in a trilogy, a story that combines science fiction, romance and adventure. The beginning of the school year is different and difficult for all students. For Naroa, however, it is even more so. Her parents have just divorced, and she has come to live in a small town from the capital after her mother got a job at an innovative pharmaceutical company called Jingko.
Naroa and her new friends from the high school visit an abandoned factory. There, they find a strange beast and decide to take it home. That will trigger a series of unexpected events, as it is not a simple otter but a boy named Gexan with the power to transform into an animal.