It's the story of a little fairy who flies into children's rooms at night and tangles their hair while they sleep. This was VERY intriguing to Juliet because we have the daily combing/torture session every morning. Her hair is very fine and somehow turns into a huge ball of tangles overnight despite my having dutifully combed and detangled it the night before. (Maybe there IS something to this whole fairy business...)
The story is simple, but like I mentioned very interesting to a three-year-old with tangly hair. It was relevant and fun and now whenever I come her hair in the morning she remarks, "I guess the knot fairy must have come to visit me last night! I didn't see her, though. Maybe I should try sleeping with my eyes open so I can."
So far, there have not been any confirmed fairy sightings, but evidence of her presence has definitely been there.