The young Mona lives in a ruined castle by the sea. She is a princess but she lives a life of misery. One fine morning a small unicorn, U, appears to her. She tells her she will help her to grow up and find happiness. The two become the best of friends until the day that a group of musicians arrive in the forest near the castle. On meeting them, Mona discovers two new things: music and a young attractive guitar player called Kulka. But what will happen to U if Mona no longer needs her?