From the mainland a threat of war looms over the people of Clouds End and the other islands, but for Brook (young girl, main character, from Clouds End) something more personal and equally dangerous is also on her mind. Something has followed her out of the mist, a haunt, a creature who has assumed her bodily shape, and the saying goes that only one twin survives, original or haunt. But before she can face her double, the forest people from the mainland have to be stopped.
If you set up a conflict like “shapechanging creature has made itself into a twin of the main character, only one can survive” you expect at least to know at the end of the novel who survives. Which you won’t, at the end both go into the mist again, one comes out and we aren’t told who it is. Which might be a smart ending for a short story, but if I invest time into a novel I want a clear cut ending, not something ambiguous like this.
Most of this novel is an okay fantasy story, nothing extraordinary but nicely told and it passes the time, but the ending really makes the whole less than its better parts.