Everybody remember how the Pied Piper saved Hamelin from the rat invasion, but somehow the second part of the tale is seldom reminded.
After he removal of the rats, the piper asked the townsmen for his reward, which was arranged before. However, the people of Hamelin refused to pay the piper, who promised revenge.
Some time later, when the people of the village were in church, the piper went back, and played a new tune, casting a spell on the children of the village. Boys and girls were hypnotized, and followed the pied piper out of the town, where they were lured into a cave and never seen again.
Quite a terrifying tale. I guess that the moral of the story is easily understandable: always pay the piper, especially when he's dressed like a stupe.