I don’t remember if I’d read this before or not. If I did, it was when I was a child. I read ‘The Princess and the Goblin’ and ‘The Light Princess’ dozens of times, and loved them. I know I also read ‘At the Back of the North Wind’ and didn’t care for it as much. I’m not at all sure I would’ve loved this when I was little, but I loved it now. It does feature the same Grandmother/Lady seen in ‘The Princess and the Goblin,’ with her magical baths. She has got to be one of my favorite characters in fiction, and even a brief appearance is wonderful. Plus, air-fish! I loved the air fish! (After having an Oscar in a tank for some years, I used to dream about fish ‘swimming’ around my room, through the air.)
Plot-wise, this is sort of a cross between a religious allegory and Plato’s ‘parable of the cave.’ Two innocents, one of whom finds a golden key at the end of the rainbow, go on a quest to find the ‘land from whence the (sublimely beautiful) shadows come.’
The story is odd and allusive, rather than didactic, and quite lovely.