The humans are the aliens on the atevi world. This is the second book in the series, and it's actually really important to read the first book, Foreigner, to get what's going on.
The differences between the atevi and humans are subtle, but even these small differences cause huge problems.
The story takes place from Bren Cameron's viewpoint. The way he constantly has to shift thinking about the world in a human way and then in an atevi way is interesting, realistic and well done.
9/10