A certain wolf could not get enough to eat because of the watchfulness of the shepherds. But one night he found a sheep skin that had been cast aside and forgotten. The next day, dressed in the skin, the wolf strolled into the pasture with the sheep. Soon a little lamb was following him about and was quickly led away to slaughter. That evening the wolf entered the fold with the flock. But it happened that the shepherd took a fancy for mutton broth that very evening, and, picking up a knife, went to the fold. There the first he laid hands on and killed was the wolf. 
The evil doer often comes to harm through his own deceit. 