River God follows the fate of the Egyptian Kingdom through the eyes of Taita, a multi-talented and highly skilled eunuch slave. Taita is owned by Lord Intef and primarily looks after his daughter, Lostris, but also plays a large role in the day-to-day running of Lord Intef's estate.
The Pharaoh of Egypt is without a male heir, and Taita inadvertently causes Pharaoh to take an interest in Lostris. Lostris meanwhile is in love with the soldier Tanus, who unbeknownst to her is hated by her father. Eventually Pharaoh marries Lostris and her father, Lord Intef, reluctantly gives Taita to her as a wedding gift.
Meanwhile, Tanus has angered Pharaoh by speaking bluntly about the troubles Egypt is in— most prominently the growing bandit threat which terrorizes all who travel outside of the major cities. Pharaoh condemns him to death for his actions, but is convinced to allow Tanus to redeem himself by attempting to eliminate all the bandits from Egypt within two years. Since his sentence is revealed on the last day of the festival of Osiris, he is to return on that day of the next festival with his task complete or face death by strangulation.
Tanus, with the help of Taita, hunts down and captures the leaders of the Shrike bandits. On presenting them to Pharaoh, it is revealed that their leader is Lord Intef. Tanus has his death sentence lifted, but Intef manages to escape before he can be punished for his crimes. After the sentence is announced a storm sweeps through allowing Lostris and Tanus time to be secretly alone together. During this time Lostris conceives Tanus' first born, and before the secret can be discovered Taita arranges for her to resume her wifely duties to Pharaoh. When the child is born he is named Memnon and claimed by the Pharaoh as his own, and his true paternity is known only to Lostris, Taita, and Tanus.
A new threat to the kingdom emerges— the warlike Hyksos. Equipped with the horse and chariot, as well as a superior recurved bow, their technological superiority is far greater than the Egyptian army's. The Pharaoh is killed, forcing a majority of the Egyptian nobility (including Lostris, Tanus, and Taita) to flee Egypt by headingup the Nile with the remaining army.
During their exile Lostris gives birth to two more of Tanus' children, both daughters, but as their relationship has been a secret Taita creates a cover story where the ghost of Pharaoh sires the child. During their period in exile, they regain their technical superiority— Taita replicates and improves both the chariots and bows he has seen used to such great effect on the battlefield.
While searching for a suitable burying place for Pharaoh's body, Taita is taken captive by one of the Ethiopian chieftains of the area— the brutal Arkoun. While in captivity, Taita becomes close friends with Masara, a fellow captive and the daughter of one of the rival chieftains. Taita eventually escapes captivity due to a freak flooding, finds the father of Masara, and strikes a deal with him to rescue Masara. With the help ofTanus, Memnon, and the Egyptian army, Arkoun is defeated. Tanus is mortally wounded during the battle and dies. Masara and Memnon fall in love and become married, with a wedding gift of several thousand horses which further boost the Egyptian army. Led by their new Pharaoh Tamose (formerly Prince Memnon), they return to Egypt. With their new-found weaponry and tactics, they defeat the Hyksos invaders and regain the upper kingdom of Egypt from Elephantine to Thebes.