2.5
I think what's going on here is just that Nimmo's writing style just doesn't align with my preferences, as I have rated many of her books low at this point. I like high-action, fast-moving books, and hers simply aren't that.
It drags on for me because most of it is narration, and the rest barely anything noteworthy is happening, save for a couple scenes.
It's not that I minded it being from Nia's point of view, I just think it took away from the main story. I wouldn't call it a waste of time, but this whole book could have been side scenes while following Gwyn.
I don't really understand what's going on half the time, to be honest. Nia had no idea her dad was trying to get rid of Fly? Why couldn't the other family be reunited prior to the kids finding them again? Gwyn didn't think that Arianwen might have been taken by the only people that could have taken her? The whole matchbox was missing, so it wasn't like the first time. Easily could have deduced that, or even asked Nia. Additionally, why would she think it's okay to hand her off rather than returning her after she found out she was stolen?
The story itself isn't bad at all, just the delivery being a tad boring if you also don't like slow-paced books.