Nuns using visions of God to persuade novices to have sex, threesomes with priests, the poisoning of a fat German princess, a prominent theologian shacking up with a vicaress, young nuns murdered, fetuses removed from an abbess, and cardinals, the Jesuit superior general, and the pope all enthralled by a beautiful and charismatic fraudulent saint—it’s enough to put The Decameron to shame.

The hard-to-believe story that contains all of these juicy nuggets—the 1858 scandal at the convent of Sant’Ambrogio in Rome—is the subject of Hubert Wolf’s rigorous and stunning new book, The Nuns of Sant’Ambrogio: The True Story of a Convent in Scandal. Translated by Ruth Martin, it is a hybrid of high and low perfect for the modern reader—racy and yet simultaneously erudite.

The level of intrigue and the variety of scandal are at some points so bewildering that it’s hard to keep things straight. So, perhaps it’s best to start with the woman who triggered the whole mess—the twice-widowed, famously corpulent Princess Katharina von Hohenzollern-Sigmaringen.

Despite health issues, Katharina was determined to join a convent. After one failed attempt, her adviser, Cardinal Reisach, suggested she join the convent at Sant’Ambrogio.

However, after a mere 15 months, in 1859 Katharina would be rescued from the convent by her cousin, the Archbishop Hohenlohe-Schillingfurst, and rushed to recuperate at his estate, Villa d’Este.

What pushed the princess to flee? According to her denunciation to the Holy Tribunal of the Sanctum Officium (the Roman Inquisition), she had discovered the convent to be a cult venerating a false saint, a hotbed of sexual intrigue, and broken confessional seals. And she hysterically claimed there had been an attempt to poison her.

The book then follows the determined and detailed investigation by judge Vincenzo Leone Sallua, who worked from 1859 to 1860 to determine what exactly went on at the convent so that Pope Pius IX could determine whether a trial should be opened. The story he uncovered was far more dramatic than the princess could have imagined, and implicated some of the most powerful cardinals of the day, the Jesuit general, and multiple popes. It was the kind of scandal opponents of the church joked about—libidinous nuns and priests run amok behind the closed doors of the convent.

This was not the first scandal for the convent. Its founder, Maria Agnese Firrao, had once been the toast of the Catholic world for her visions and healing powers. The former pope, Leo XII, considered her a close spiritual adviser, as did numerous cardinals and the king of Sardinia. She was later found out to have fraudulently claimed to have performed miracles, had an affair with her confessor, had two abortions by the church when she got pregnant by clerical officials, engaged in a threesome with her confessor and another nun, and encouraged her novices to venerate her as a living saint. The Vatican publicly denounced her for her actions, and stripped her of her abbess title. However, that same Leo XII issued a brief in 1829 largely exonerating Firrao from the 1816 Inquisition verdict.

One of the sins the princess charged the convent with was that the nuns were venerating Firrao, a false saint. She was right, Sallua discovered to his horror, but there was also a rival for the nuns’ adoration.

Maria Luisa, at just 27 years of age, was the convent’s alluring novice mistress and vicaress. It turns out that Maria Luisa, who Katharina accused of the poisoning, was seen as an upstart fraud by the founder Firrao. She claimed to have visions from Mary and Jesus, and the nuns at the convent—including the abbess—believed she had miraculous powers. However, as Sallua discovered, she was a monster who used her supposed visions to entice novices into her bed, embezzle convent funds, and poison opponents.

One nun, who was luckily exiled and not killed by Maria Luisa, told Sallua that Maria Luisa claimed the Lord told her in a vision she needed to treat a sickness in the nun’s private parts. She claimed that another vision had told her that a liquid that came from the Lord “flowed over my whole body, collecting in the lower part of my body, as in a little hollow where it then remained,” and that they should share in this liquid.

Another nun confessed that Maria Luisa was “keen” on something she called “giving,” which involved asking “me to lie in a certain position, with my legs raised, while she “entwined” herself with me … she then made movements and a sound such as I cannot express in words, and she instructed me to position myself so that I could receive her bodily fluids into me.” Or, continued the nun, “she wanted me positioned above her, so that we were body to body and mouth to mouth.” Maria Luisa told this nun that her bodily fluid was a gift from God to heal the nun’s sickness. She also created an initiation rite in which novices had to sleep with Maria Luisa the night before they were made nuns, made to “lay face-to-face and breast-to-breast.”

However, in a twist of events that will be unsurprising to modern audiences, when Maria Luisa confessed to these actions, she also disclosed that she had once been a victim, and that Firrao herself had once done the whole this-liquid-in-my-privates-is-from-God routine to her when she was a novice.

Maria Luisa also admitted to trying to poison the princess, who had figured out that Maria Luisa was less than saintly. She gave the princess gruel with ground glass, tartar emetic, and opium in an attempt to kill her. While Katharina would suffer (she passed what Wolf believes was stomach lining in her excrement), the portly princess survived. So Maria Luisa went about killing off her accomplices. One of them survived. Three others—one 21, one 22, and an elder nun—were not so lucky.

Wolf’s book, and the story of Sant’Ambrogio, are not merely concerned with tales of lurid sexual escapades. Sant’Ambrogio was also at the center of a significant theological war within the Catholic Church, as influential players in that war were ensnared in its drama. The scandal and its aftermath also highlighted a degree of unfathomable leniency when it comes to grave crimes committed by members of the church—again, something all too familiar to modern readers.

As Sallua finished his investigation into the nuns, he turned to the two Jesuit confessors, Giuseppe Leziroli and Giuseppe Peters, who Katharina accused of being in league with Maria Luisa and of breaking the confessional seal.

The investigation into Leziroli revealed that he had continued to venerate Firrao in spite of the Inquisition’s decision that she was a fraud. However, the investigation into Peters proved far more rewarding, and problematic.

Maria Luisa had admitted to a full-blown sexual affair with Peters, as well as confirming his role in supporting her manipulation of the rest of the convent via the confessional. But Peters was in fact not his only name—he was actually Joseph Kleutgen, one of Rome’s more prominent theologians, whose writings influenced everyone from the Jesuit Superior General to conservative cardinals to the pope himself.

Kleutgen hailed from the wing of the Church most determined to reinforce papal authority through theological dogma in the aftermath of the Napoleonic Wars (the notion of papal infallibility, for instance, originated in this time period). Kleutgen and his allies, which included the aforementioned Cardinal Reisach, were opposed within the Curia by none other than Katharina’s cousin, the Archbishop Hohenlohe-Schillingfurst. Kleutgen had also used Maria Luisa’s visions, which were believed by the Jesuit Superior General, to expose the homosexual relationship of two theological rivals within the order.

Now Kleutgen and his work were being undercut by his own deeds. In one honest to goodness laugh-out-loud section of the book, Kleutgen defends his sexual affair with Maria Luisa with the theological argument that the sex he had with her was without lust and so therefore was not a sin.

Maria Luisa, quite simply, was guilty of embezzlement, sexual abuse, and murder. This was explicitly aided and abetted by her Jesuit confessor Peters (the theologian Kleutgen). But their guilt also undermined the authority of the papacy just as it was trying to consolidate it. When it came time for their sentencing, they were each to be “imprisoned” in a monastery or convent. While Maria Luisa might have faced the death penalty and Kleutgen a heavy sentence in most secular societies, Pope Pius IX actually reduced their already lenient sentences. After much debate, Kleutgen was “imprisoned” for three years, which Pius reduced to two—which Kleutgen served at a house of retreat on Lake Nemi. One of the cardinals involved had actually wanted no punishment for him. Maria Luisa was sentenced to 20 years, and Pius reduced it to 18. This came after multiple attempts by Pius to suppress or avert a full-blown investigation into the convent.

Wolf largely avoids a direct comparison between the 19th century scandal at the convent, the leniency of punishments, and subsequent attempts to keep it under wraps and the 20th century priest abuse scandals. However, it’s hard to read the book without that hovering in the mind. Maintenance of the Church’s image and preservation of those in power took precedence over justice for murdered nuns and sexually abused novices. The decision by the Jesuit order, even its own historians, to downplay or erase the affair from works about Kleutgen or this time period is especially disheartening. “This damaging picture—the father of new scholasticism as a criminal and seducer, and the Jesuits and their friends in the Curia as a society of gullible bigots—should on no account be allowed to enter the public imagination,” writes Wolf, when taking stock of why the Jesuits were not open about it.

After Pope Pius IX reduced the sentences, Wolf makes his views clear, writing, “Was two years really an appropriate punishment for the serious offenses Kleutgen had committed? It’s clear where the pope’s sympathies lay in this trial … the padre was part of his Jesuit network. Kleutgen and the Jesuits shored up the pope’s sovereignty—this called for care and leniency.”

Wolf manages to check so many boxes for anti-Catholic Church fans that the book could be mistaken for a complete indictment of the Church. But that would miss one of the greatest ironies of the book—that of the refreshing dedication of the Inquisition’s investigating judges. While popular history associates it with gruesome torture, the Inquisition in Wolf’s telling treats issues of faith with such exacting skepticism that it feels like watching an atheist at work. And with a book filled with a scandal this explosive about an institution so important to so many people, that kind of balance that Wolf provides is reassuring.