We first see Ullmann done up in hideous Pippi Longstocking pigtails, presumably the look du jour for ninth-century teen messengers of God. When both her parents die, orphaned Ullmann announces her intention to go to a nunnery. Her father's randy monk pals won't hear of it, however. As one of them puts it, "You weren't meant for a nunnery, Joan!" And to prove the point, they all gang-rape her. In a response that would suggest she has more than a passing fancy for medieval religious practice, Ullmann likes it.
Sticking with her plan, Ullmann enters the convent Our Lady of Deceptively Meek Overactors. Things heat up quickly when the emperor Charlemagne stops by one night for dinner, bringing along his grandson, Franco Nero. Nero instantly lusts after Sister Liv, but still unfamiliar with how the church hierarchy operates, she refuses him. She does, however, watch Nero have sex with Sister Lesley-Anne Down, after which she hurries off to her room to masturbate.
Ullmann's next religious experience occurs when the convent is deemed in need of redecorating -- it's SO eighth century -- and the emperor sends over painter Maximilian Schell, a studmonk of the first order. "Why are you a monk?" Ullmann asks, to which he responds leeringly, "It's the only way I could get myself into a nunnery." Sister Liv sees the light and succumbs to this inspired member of the clergy. "Do you think it surprises our Maker that we have sinned?" Brother Schell asks rhetorically afterward. "It's the only thing that separates us from the angels."
While Sister Liv is still, no doubt, digesting that bit of theological wisdom, the emperor dies, prompting barbarian Saxons to rape the nuns. Schell spirits Ullmann away and, in the interests of her future safety, gives her a boyish haircut and a new identity -- Friar John. Her butch makeover wins Ullmann twice as much attention as she got before -- from men. Soon-to-be-emperor Nero, for example, likes the looks of this "lad" so much he ordains him/her a priest.
Pope Trevor Howard is attracted too, and anoints him/her a cardinal. When Cardinal Ullmann calls on the Pope in his spa and finds His Holiness wearing nothing but a towel, the Holy Father vamps, "You look splendid," before plunging buck-naked into the pool, shouting, "Shed those magic robes!" Ullmann demurs, but the Pope carries a torch for his special servant of God right to his own deathbed, on which, eyeing Ullmann-in-drag hungrily, he designates him/her as the next Pope.
When Schell sees Pope Ullmann in full papal drag, he's moved to hit on him/her all over again (is this what's meant by catholic tastes?). Schell's charms don't work, because Nero is on the scene ready to be made emperor. After Ullmann crowns him, he recognizes her and says, "Odd if the Pope should be a woman. There are those who would say it showed the hand of the Devil. I've always had a weakness for the Devil!" Soon the emperor and the Pope are going at it in an admirable display of harmony between church and state. But then Nero goes off to fight the Holy Wars, leaving the Pope to mope about the Vatican. Months go by until one day, Pope Liv, now mysteriously swathed in enough robes to outfit the entire Jesuit and Franciscan orders, walks out amid his/her faithful in celebration. It proves an untimely show of papal authority, for suddenly the Pope collapses on the cobblestones and gives birth to his/her illegitimate love child. Appalled at the enormous deception that has been perpetrated, the crowd tears Ullmann to pieces. So did the critics.