Ada is able to talk to a ghostly mouse like Ishmael. But this is nothing to wonder about, after all she lives in the huge castle of Ghastly-Gorm Hall. As Ada is allowed to keep company with her father only once a week, every distraction is welcomed by her. When she begins to search for mousetraps with Ishmael, they discover something strange. Every year Maltravers, her father’s creepy indoor gamekeeper, has to see to new creatures for the hunt unless he is busy with other things.

This year, however, he seems to plan something really mean. On their nightly excursions Ada and her new friends Emily, Ruby, William, Kingsley and Arthur find a trapped siren, three harpys, a centaur, a faun and two orang- utans clad in dresses and they realize that they finally have to do something against this year’s hunt. But what?