Ilario is a hermaphrodite born in Iberia, child of a rich noblewoman who exposed him to save herself from the shame of having engendered a "Monster" child. Luckily, Ilario is found by another family, and sold into the King's court, where s/he grows up as the court freak, being neither wholly man nor wholly woman but an unnatural mixture of both.
In Ilario's free time s/he takes up drawing and painting, and when Ilario is finally freed by the King to raise money for the dowry of one of the Royal Princesses, Ilario takes ship to Carthage, where s/he may draw, paint and limn the particular sky there, which has had no sun for over 200 years, and is illuminated by a strange combination of Auroras, Coronas and strange veils of light.
A chance meeting with a guard at the gates brings Ilario to the guard's home, where the man makes love to him both as a man and a woman. Shortly afterward, the guard's mother brings Ilario a meal, which is drugged, and Ilario is sold into slavery.
When Ilario wakes up, s/he tells the slavemaster that s/he is a painter and scribe and can read and write. Ilario is sold to Rekhmire', an Egyptian Eunuch who goes around buying up books and treatises for the library in Alexandria. Rekhmire' has sympathy for Ilario, who is as damaged physically as he is. Unlike Ilario, Rekhmire' chose to be a eunuch, and became one after he went through puberty, so unlike the popular image of the fat, lisping, high-voiced eunuch, Rekhmire' actually looks like any normal man, except for the lack of balls.
From the start, Rekhmire' treats Ilario more like a friend than a slave. But Ilario is hunted by his mother, who wants to kill him so that the threat to her honor and station can be expunged without evidence. Rekhmire' shows up as Ilario confronts his mother, and charges her with attempting to steal and kill his slave. He hopes that when he formalizes his charges before Carthage's magistrate, word will get back to Iberia, and end the threat of Ilario's mother once and for all.
But Ilario then becomes a pawn in the hostilities between Carthage and Iberia. Carthage wants to hold onto Ilario so that his mother cannot say the charges are false and there is no witnesses. Rekhmire' tracks down Ilario's actual father, who accepts him for who and what s/he is, and Ilario makes plans to sail for Rome, slipping out of the city with Rekhmire' while his father returns to Iberia to placate the King.
When Ilario goes to Rome, he is able to apprentice to a painter who is teaching a new style of art, Art as seen in perspective. S/He learns a great deal, but has a falling out with the master when Ilario falls in love with a girl whom the master had once wanted to marry, but was rejected by her family. Ilario meets her, and falls completely in love. She is also damaged, having a club foot, and Ilario charms her by telling her of his/er travels and offering to take the girl along. Ilario doesn't tell the girl of his/er own physical abnormalities, and they are married by a bribeable cleric.
The girl is an Etruscan, and must be purified for three days before the marriage can be consummated. Ilario agrees to wait, and tries to make up with the Master Painter. Before they had their falling out, the master had been comissioned to paint an animate statue, a golem. The Golem has so intrigued the painting master that he has decided to steal it, with Ilario as his unwitting accomplice. Unfortunately, the Golem has orders about being taken away, and grabs the painter, who struggles and is rather unfortunately killed. Ilario is injured when he tries to run, but Rekhmire' and he manage to hush it up with the help of the Egyptian embassy, who owns the golem to begin with. Making the painter's death seem an accident, they plan to flee to Venice with Ilario's new bride in tow, but when she sees the truth of her new "husband", she is repulsed and rejects Ilario.
Before Ilario and Rekhmire' can leave Rome, Rekhmire' has Ilario examined by a doctor, concerned over the head injuries inflicted by the golem. Ilario will be fine, but is stunned to learn that herm encounter with the guard had other consequences. Ilario is pregnant.
Now disguised as a woman, Ilario and Rekhmire' travel to Venice and are met by Ilario's father, who accuses Rekhmire' of impregnating his daughter/son. Worse for Ilario is that his mother and step-father are in the city, along with their children, and have brought an assassin disguised as a secretary who is charged with killing Ilario.
Howver, that isn't the only danger in the city of canals, and Ilario, Rekhmire' and Ilario's father are attacked twice on their way to their new lodgings. Ilario is injured, and Rekhmire' is shot in the knee, trapping them in the city while the wound heals. Since travelling while massively pregnant is going to be impossible, as well as dangerous, Ilario must fend off her former family with politics and diplomacy until they can move on. But even with herm father's troops and his own presence, staying alive isn't going to be easy.
This was an unusual book, and Ilario is a very unusual character. Mary Gentle managed to get around the problem of pronouns to describe Ilario by having the book be told from Ilario's point of view. As you can see, just from the review above, using his/her or "herm" is extremely unwieldy.
I must point out that one of the reviews for the book, printed on the cover, manages to be extremely misleading. It says, "This action packed, deeply intelligent novel [is] a focus for intrigue, intellectual debate and a fair amount of polymorphous hot sexual action." (From Time Out London). From the way it's stated, either the reviewer thinks that hermaphrodites are going to be getting lots of hot sex because of this book or that a lot of sex goes on in the book, involving the main character. I counted exactly two acts of sex, and both occured in the first six pages of the book. Ilario states the intention of having lots of sex, but being sold into slavery puts rather a decided crimp in those plans. And Rekhmire' does ask if Ilario will consider a sexual relationship with him as part of his bondage, but Ilario says no. That's the only described sexual relationship involving Ilario in the entire book! Not what I would consider "a fair amount". Anyway, realize that this is misleading, for those who care about those sorts of things.
Ilario's world is not ours. In fact, one could say it is a fantasy version of our own: Rome has no Pope because the Papal Seat was cursed, the city of Carthage still exists in the era of Christianity, we have the "No-Sun" area over a fair bit of North Africa, and so on.
Also, Ilario is not an exceptionally decisive character. More things happen simply because of Ilario's presence, and because herm existence is a threat to Ilario's mother and stepfather. Also, because Ilario was raised a slave and never had to make a decision more important than what was for dinner or when to go to bed. Still, it's possible not to notice this as Ilario is pulled along by circumstance, luck, unluck and fate. It does make the story very strange and not the usual sort of book I read.