Not really Wells' best work, IMO, but still head & shoulders above most of what's out there.
Moon is a shapeshifter, living among yet another group of humanoid "groundlings" and hiding his other-ness, as he has done for many years, ever since his mother and siblings were killed. Every time he starts to get comfortable, someone discovers he's different, and he has to move on, usually in a big hurry - unfortunately, there's a race of malevolent shapeshifters called the Fell that regularly prey on groundling communities, and Moon has the misfortune to resemble, in his other form, the ruling type of Fell. Moon doesn't know *what* he is, but he knows he's not one of them.
By the way, Moon's other form is dragon-ish. Think wings and claws. So although he's not evil, it's easy to see why his transformational abilities make his neighbors nervous.
Unmasked once more and about to be executed, Moon is rescued by a huge, winged monster - Stone, who turns out to be an elder of Moon's own race, whom he tells Moon are called the Raksura. But Moon is skeptical of trusting Stone - too many instances where letting his guard down the slightest bit has meant loss of any safe haven, and usually physical danger. Dispossessed, and understandably curious, he accompanies Stone on his journey homeward. There, Moon is introduced to the two classes of creatures that constitute the Raksura: the Aeriat, winged warriors and rulers; and the Arbora, non-winged hunters, teachers, soldiers, artisans, and "mentors" (a sort of shaman/healer class that also act as advisors to the queens and their consorts), and discovers that Stone has a hidden agenda for bringing him there.
The "orphan's quest for identity" is a fairly standard fantasy theme - Wells' strength here is the unusual societies she has created. Would have preferred a bit more time and care spent on fleshing out the personalities of the various main characters, but overall, very satisfying.