Moon is different from the people he lives with and hides a terrible secret - after the death of his family years earlier, Moon has been alone in a world where he doesn't quite fit in, living with people who superficially look like he does, moving from place to place when they get too suspicious about him. Moon is a shapeshifter, able to fly in his other form, and when his secret is discovered he finds himself with an unexpected ally and a possible place to call his own. Except that this new place is under threat, a threat that may have links with Moon himself, and he is understandably cautious about embracing his new people given his past history.
I've read a couple of this author's books previously, those set in the world of Ile Rien which is quite like our own, except with magic added. The world in which The Cloud Roads and its accompanying books is set takes another step to the side from those more-familiar kinds of fantasy books into a place where nobody looks like us, and since they aren't human, why should they?
Given the differences between that world and our own, the skill of the author in terms of both world-building and character creation really comes into its own. In The Cloud Roads, its groundlings and Raksura - not to mention the Fell, who are the villains of the worlds in which these books are set - it's very easy to empathise with the characters and care about their fate. Often books are let down by characters doing stupid things, solely as a way of driving forward the plot, and this doesn't happen here. Moon and the other characters in this book behave in ways which are understandable, given their respective experiences and worldview and I found that I needed to know what would happen to them in the longer term.
This is the first in a series of books set in this universe - a trilogy of novels so far and also a couple of books of novellas - the series continues with The Serpent Sea, which I already have so will probably be reading shortly!