The Pied Piper of Hamlin

A grandfather relates to his two grandchildren, the story of the township of Hamlin which was plagued with rats. In their moment of desperation, a stranger, a Pied Piper, appears with a promise to rid the town of rats forever in exchange for 200 gold bars. The Piper fulfils his promise by playing magical music which attracts all the rats as he led them to the river to drown. When the townspeople fail to keep their promise and pay him only 1 gold bar, he vows revenge - and delivers... The moral of the story - Always keep your promise - always pay the piper.