A Sultan from Syria hears of Constance, a Roman princess in Rome who is said to be the goddess of beauty, grace, and innocence. The Sultan promises to convert to Christianity if married to Constance.
The marriage is arranged against Constance's will and the Sultan converts to Christianity. His mother is angry over her son's betrayal on their religion. She orders her knights to kill everyone who is Christian.
Constance lands in a pagan land, Northumberland, and meets a constable and his wife, Hermengild, who take her in. Constance coverts Hermiengild and her husband to Christianity . A lustful knight notices Constance but is rejected by her so he kills Hermengild and makes it seem as if it was Constance.
The king, Alla, made the young knight swear it was Constance on a holy book, but, since it was the knight, he died instantly. The miracle pushed the people to convert to Christianity.
Constance and King Alla get married. Alla goes to war and has a baby. Alla's mother, who does not like Constance and tricks her into thinking Alla does not want the baby. Constance sails on a ship away from Northumberland and is returned to Rome by a Roman ship.
King Alla ends up in Rome and reunites with Constance along with Constance reuniting with her father. The family return to England and in the near future, Constance and Alla's son becomes the Emperor of Rome.