One day, many parents received a letter from the school, with the following wording: "To the parents! It is you who are concerned - It is you to whom I want to speak about the responsibility of parents towards their children, so I ask you to come to the Odd Fellow Palace on Friday the 22nd at 8 pm and hear what I have to say to you."

A woman is found strangled in her shop. Shortly after, another murder is committed. Perhaps the most terrifying is that the both girls' name is Sonja. The police is convinced it's the same killer and at each scene is heard a woman singing the same song. A song which is soon dubbed the 'murder melody.'