Pied Piper of Hamelin
The Pied Piper of Hamelin is a German legend from the Middle Ages about a mysterious, multicolored stranger who comes to the town of Hamelin (a real town, now Hameln) and offers to rid the town of the rats that are plaguing it. After an agreement, the piper magically lures the rats away with his playing, leading them into the nearby Weser river where they drown. But the town refuses to pay him, and in revenge, the piper then lures the town's children away to a nearby mountain or cave, where they all disappear, never to be seen again.
The legend has been told, retold, embroidered, altered, added to, et cetera; the earliest versions don't even have the rats! But there is some historical fact buried at the heart of it all. The current best theory is that "children of the town" was a way to refer to ANYBODY from the town, not just kids. Then a large group of townspeople were recruited to move to Eastern Europe to repopulate the area after it was decimated by Mongol invasions.