A young Christian noblewoman is determined to live her life as a virgin. When forced to marry, she converts her husband Valerian and his brother-in-law Tiburtius to Christianity, and they live their lives in chastity.
The pagan prefect Almachius declares that everyone must worship at the shrine of Jupiter or die. Tiburtius and Valerian lose their heads when they refuse, but make a few converts in the process. Angered at the defection of so many pagans, Almachius calls Cecilia before him. He tries to convince Cecilia to bow to his power and worship his gods, but she refuses, making a fool of him in the process.
Almachius has Cecilia boiled alive then decapitated, but the executioner fails to get the job done. Cecilia remains alive for three days, preaching and teaching the Christian faith. After her death, Pope Urban consecrates her home as a shrine.