In December 1452, six months before the fall of Constantinople and the end of the thousand-year Byzantine Empire, a stranger arrives in Constantinople, a "Latiner," who calls himself Jean Ange in French and Johannes Angelos in Greek. His origins are shrouded in mystery; all that is known is that he has spent a long time at the court of the Ottoman Sultan Mehmed. Johannes joins the defenders of the city and becomes the closest associate of the Genoese mercenary commander Giovanni Giustiniani, who has placed his soldiers in the service of the Byzantine Emperor, as the overwhelming Ottoman army is expected to attack at any moment. Johannes falls in love with Anna Notaras, the daughter of the leader of the pro-Turkish faction at the Byzantine imperial court. He eventually reveals to her the secret of his origins. The novel, written in the form of a diary, depicts this story.