For those who thought the simplistic morals of Grimm tales were just for kids, "The Pied Piper of Hamelin" will probably convince you otherwise. In addition to its dark content, this is a cautionary tale about governance as well as taking responsibility for financial agreements.
The story takes place in 1284 in the Germanic town of Hamelin (now known as Hameln). At this time, the town was suffering from a severe rat infestation. The town and its mayor were at a loss when a stranger came into town. He wore slightly bizarre, pied (multicolored) clothing and carried a musical pipe. He told the people he'd heard about their rat problem and that he could rid the rats from the town -- that is, in exchange for a fee.
After agreeing to the sum, the piper took out his instrument and started playing a ditty. His song magically lured the rats to him: They came running and congregated around him. After he was convinced that he'd attracted all of the town's rats, he walked toward the nearby Weser River. There, with the rats following him all the way, he walked right into the water. The entranced rats continued blindly and dove right in, where they all drowned.
The townspeople celebrated, but they refused to pay the piper what they promised. He left, furious at the villagers and planning retribution. He got his revenge on the fateful date of June 26, which was both Saint John Day and Saint Paul Day. Dressed in hunter's attire and a red hat, the piper returned to the town, playing another song on his pipe. When the town's children heard the tune, they all flocked to him, in a similar trance as the rats. The children followed the piper out of the town and to a mountain cave, where they were never heard from again. Interestingly, the Grimm story makes a note that the mayor's grown daughter was among the group of children, which readers might infer was an act of revenge aimed directly at the mayor.
The Grimm brothers go on to say that the townspeople put an inscription on the town hall to commemorate what happened.