Hula-Hopp, Conny plot
Diana Haller (Nicoletti) owns a music store and her teenage daughter Conny (Froboess) plays in a band that regularly performs in the hall 'Das bunte Krokodil'. dr. Berning (Juhnke), who is involved in the student exchange between Germany and America, thinks the Haller family is ideal for housing American student Billy Newman (Gildo) with the Hallers. Billy wants to finish his music studies in Germany. Besides, Berning thinks Conny is a boy. No sooner said than done, while Conny dresses up as a boy to avoid being fooled. When John Newman (Vogel), Max's father, comes to visit and finds out what's going on, a major scandal seems to have arisen. Billy shows that he was aware of the matter from the start and is now in love with Conny!