The book tells the story of a little monster named Ni, who lives in Gulou, the ancient drum tower in Beijing. He is one of the 10 house-ridge beasts used to decorate eaves in ancient Chinese buildings. In the story, though he is free as a bird, Ni is eager to find a partner who is similar to himself and wishes to find a complete confidant. Every good friend he finds, they all resonate with him, but they're not exactly look like him, so he gets frustrated again and again. And when he finally meets another house-ridge beast, he finds out that the difference between them is so big that they can hardly be friends. At that time, he realizes that he and his good friends all love Gulou from different angles, which is the common ground of all of them. It is the similarities that make them friends, and the differences between them make everyone special. He begins to learn to appreciate the specialities in others, as well as his own.