A witch found two children playing beside a river and stole them away. They succeeded in escaping one day, but the witch set off to bring them back.
A good fairy who was passing by saw the children and took pity on them. She set a great ring of fire around them to keep them safe. But the witch managed to blowout the flames.
So the fairy built round them a high wall of glass so smooth it could not be climbed. The witch returned to her house to find a hammer to break it with but when she returned the fairy had spirited the children away and they were safe at home.