Based on

Movies like Piraten auf der Pferdeinsel (1963)

Horst, a young boy from Berlin, spends his holidays with the "Pirates" at Horse Island. The teen gang is led by Horst′s friend Benno. Soon, Horst realizes that the pirates create a lot of nuisance. Gudrun, whom Horst meets on his way to the village, tells him that she has been attacked and injured by the pirates when she tried to observe a rare cormorant. Gudrun and Horst become friends. Since Benno is less than thrilled about this friendship, he plots a second attack on the girl.