Germany, the ninth century. The young, talented Johanna rebels against the medieval rules forbidding women to learn. When her brother, Johannes Anglicus, is brutally murdered in a Viking attack, Johanna seizes her chance.
She takes his cloak, assumes his identity and enters the monastery of Fulda. As Brother Johannes Anglicus, Joan stands out as a brilliant priest and healer. She ends up in Rome, where she goes to work as a doctor in the papal residence under the name Johannes Anglicus, disguised as a man. There she takes care of Pope Sergius until his death. To everyone's surprise, she is chosen as his successor, but this highest ecclesiastical office comes under pressure when Gerold shows up in Rome. Joan must choose between her love for the Church and Gerold.
At the time of her election as pope, she was pregnant with Gerold.
No one knew she was a woman until, after a pontificate of two years and a few months, she gave birth to a child in a procession. She died on the spot. Subsequent papal processions avoided that place.