It's not very often that you come across an historical novel that portrays events from the vantage point of a eunuch. It's not the easiest perspective for an author to immerse themselves in, but Renault pulls it off with convincing surety.
The narrator of The Persian Boy is Bagoas (based on a real historical person), who was a favorite of Persian king Darius III and went on to become the erômenos or beloved of Alexander the Great. Not much is known about him beyond that but Renault makes him into a very real character, with his own passions and motivations.
The perspective on Alexander the Great is also very interesting. Not everyone may agree with Renault's interpretation, but never-the-less, this is quite possibly the most nuanced and thorough fictional rendering of a very mysterious and complex man.
The complicated emotional triangle between Alexander, Bagoas, and Hephaestion is adroitly imagined. There is some definite homosexuality, some sensuous scenes of such, but nothing particularly explicit.
It's not all psychological drama though, there's plenty of action and colorful battle scenes to keep the reader turning pages. As historical novels go, this one is well above average.