In the Highlands, fairies were known to steal women, generally right after childbirth, so they could suckle the sometimes ailing fairy infants. John Campbell reports in Superstitions of the Highlands and Islands of Scotland that a man from Loch Sunart lay down for a few minutes rest by the bed in which his wife and new infant lay. When he awoke the woman and baby were gone. Afterwards, the woman explained that they were taken up to the "Black Door", a way into Beinn Iadain. On entering the mountain, widely believed to be an abode of the fairies, they found a large company of people.
A fair-haired boy among them came and warned the woman not to eat any food the fairies might offer, but to hide it in their clothes. He said they had got his own mother to eat this food, and in consequence he could not now get her away. Finding the food offered her was slighted, the head Fairye sent off a party to bring a certain man's cow. They came back saying they could not touch the cow as its right knee was resting on the plant bruchorcan (dirk grass). They were sent for another cow, but they came back saying they could not touch it either, as the dairymaid, after milking it, had struck it with the shackle or cow-spancel (buarach).
The woman appeared to her husband in a dream, telling him that by going to the Black Door with the handkerchief that she married him with, with three knots tied in it, he could recover her.
The man tied the knots, took the handkerchief and a friend with him, entered the hill at the Black Door, and recovered his wife and child. The fair-haired boy accompanied them for some time and distance from the Black Door, but he did return to the hill for his mother was still there and they are still there now in all probability.
The protective magic used against the fairies is of great interest. Bruchorcan, or dirk grass, was probably dangerous to fairies because of it's association with dirks (daggers), that will be iron. Alos the cow-spade or shackle was also probably made of iron and had the same result. The knots, much used in witchcraft to trap or inhibit, may simply have frozen any action purposed by the fairies. The warning against eating fairy food, an act which put people in their power, features in numerous fairy abduction stories, testimony to it having been an old and widespread belief.