According to the motto “What our parents have not expressly forbidden is allowed!” Peter and Christian - both 19 years old - go on a sailing trip together on the Weser Canal. On the way, the two manage to save a boy named Abel Untermühl from the river. Abel is from Berlin and has been traveling with his boat that has now capsized for three weeks. The happy boy, henceforth on board, delights the others with his harmonica. One night the three young men discover a beacon in the North Sea and are just able to save a young girl named Corinna, who got stuck with her dinghy on a sandbank. Peter and Christian are equally enthusiastic about the girl, who, however, loves a man named Harry. Soon the young Abel also feels feelings of love for the first time, which he tries to express with his harmonica. Can he succeed in winning Corinna over or does he have to get over the first lovesickness?