After spending 15 months in captivity in a run-down brothel in the Italian city of Torino, Wealth finally saw her chance to escape. The 23-year-old Nigerian had scraped together nearly 50 euros in tips from a couple of regulars and so one winter afternoon, with her madam absent, she decided to slip out the door. It was her first time outside in months. She stopped at the local grocery store, where she spent everything she had on chocolate and cakes. For several minutes she huddled outside, gorging on the sweets and forgetting, just for a moment, the shame, humiliation and torture she had endured ever since arriving in Italy for what a friend had falsely told her was going to be a job selling African food and trinkets.

A college graduate with a degree in laboratory science, Wealth, like millions of other young Nigerians, had been unable to find a job in her hometown of Benin City in southwestern Nigeria. Beguiled by accounts of easy money in Europe, she contacted her friend’s boss in Italy, who offered to pay her travel costs up front. Wealth, who asked to go by the English translation of her first name in order to protect her privacy, agreed to pay the sponsor back out of her wages. Before she left for Italy in 2012, she swore an unbreakable oath, conducted by a ‘juju’ priest, to pay back her soon-to-be boss and madam and never betray her.

Yet when Wealth arrived in Italy her new boss told her how much she owed—65,000 euros, or $80,000—and showed her the red light district where she would be expected to work off her debt. Wealth, small but determined, refused to walk the streets. Her madam locked her up in a bedroom and sent clients to her instead. Wealth was forced to service several men a day, sometimes several at once, she tells TIME in an interview. When she escaped, she had worked off a third of her debt. Another three years, she figured, and she would be free.

Eziza, a juju priest, near his shrine outside Benin City on March 23. Lynsey Addario—Verbatim for TIME

Wealth is just one of tens of thousands of young women from Nigeria who have been trafficked to Europe for sexual exploitation over the past 15 years, according to the Nigerian National Agency for the Prohibition of Trafficking in Persons (NAPTIP), which was founded in 2003 to combat the problem. The International Organization for Migration estimates that 80% of Nigerian women traveling to Libya and attempting to then cross the Mediterranean are being trafficked into the European sex trade. Most, like Wealth, are from Nigeria’s southwestern Edo State, and its capital, Benin City, where a combination of poverty and lack of opportunity have driven thousands of young women, who are expected to financially support their families, to seek their fortune abroad. But it is that primitive oath—the ancient ritual Wealth participated in before she left Italy—that keeps many young Nigerian women bound to the sex trafficking trade, desperately afraid of the curse that might befall them if they break its terms.

The power of the “juju” curse shouldn’t be underestimated, says trafficking expert Siddharth Kara, director of the program on Human Trafficking and Modern Slavery at the Harvard Kennedy School of Government and author of Sex Trafficking: Inside the Business of Modern Slavery. It makes the sex trafficking trade particularly lucrative and nearly impossible to prosecute. The oath-taking ceremony, conducted by a ‘juju’ priest and performed in front of a carved wooden idol, is typically accompanied by animal sacrifice and incantations. In Wealth’s case, she offered up snippets of her fingernails, pubic hair, menstrual blood and undergarments, which the priest bound into a small bundle and blessed. As long as the bundle remained at the shrine, Wealth would be bound to her oath. If she broke it, she would be cursed.

That winter afternoon, as she dusted the last few crumbs of chocolate from her hands, the Italian police pulled up and asked to see her documents. She didn’t have any. When they couldn’t get through to the only contact number Wealth could provide, that of her madam, they deported her to Nigeria within days.

Wealth should have felt liberated. Instead, she was terrified. When Wealth’s former madam tracked her down a few months after her return to Nigeria, she felt like she had no choice but to return to Italy. “It was a terrible fate, I know. But I wanted to pay off the debt. If I didn’t, the curse would hunt me down, kill me, kill my family,” she says, speaking to TIME in Benin City. In January 2014, forged paperwork in hand, she boarded another flight bound for Europe, traumatized by memories of what she was returning to, but also petrified by the thought of breaking her oath.

“The level of control achieved by these oaths is greater than anything I have seen in any other human trafficking context,” says Kara. “You could not invent a better system for control and coercion. You have them believe that their spirit, their soul, their womb—everything—is under the threat of an irrefutable, irrevocable curse unless they do what they’re told.”

Children watch Ayelala Juju priest Godwin Okeh at his shrine in Benin City on March 23. Lynsey Addario—Verbatim for TIME

But the power of the oath is now under assault from an unexpected origin: the traditional ruler of the Edo people, Ewuare II. The Edo people, like other groups in West Africa, have long practiced a set of traditional rituals involving local deities and priests, which European colonizers called “juju.” Today, the ancient religion is still practiced alongside Nigeria’s more recent Christian and Muslim traditions.

As head of the 800-year-old Kingdom of Benin, Ewuare II—who was crowned the new Oba in fall 2016—wields absolute power over the deities and priests who practice juju today. On March 9, the Oba convened a meeting of some 500 juju priests and practitioners at his palace to cast a curse of his own. To underscore the gravity of his pronouncement, the Oba brought out a religious relic, a carved wooden representation of an important deity that hadn’t seen sunlight for more than 800 years. He then nullified any oaths undertaken by victims of human trafficking and placed a curse on any native doctor or juju priest who carried out the practice. It was, in the words of one of the meeting’s attendees, the nuclear missile of curses.

The Oba’s curse will no doubt stop the oath-taking ceremonies, despite the fact that they are the principal source of income for many traditional priests, says Solomon Okoduwa, Senior Special Assistant to the Governor of Edo State on Human Trafficking and Migrants. Priests are already pleading with families of victims to come to their shrines to collect their bundles of intimate items. So powerful is the Oba’s curse that few will even admit they ever conducted the oaths, even when presented with video evidence to the contrary. (One priest offered to show TIME the oath-taking ritual, if provided with the requisite sacrificial offerings of one goat, one cockerel, kola nuts, and a calabash, but swore he had never conducted one himself, despite the fact that investigators had already identified him to TIME as the oath taker in several trafficking cases).

Still, Okoduwa is not convinced that trafficking will stop entirely. “There is simply too much money to be made,” he says, as he lays out the considerable return on investment for most traffickers. It costs traffickers around $2,000 to get a woman from Nigeria to Italy via the Libya route; priests charge traffickers $1,000 for the oath-taking ceremony in addition to the sacrifice materials. But once in Europe she can earn her traffickers anywhere from $35,000 to $80,000 before she is free of her debt. Usually, the trafficked women stay on in Europe to earn money on their own, before returning home with enough funds to buy a house, start a business or support her family. Often the returnees become madams themselves, flaunting their wealth to lure new victims to Europe and perpetuating the cycle. The luxurious homes of some of the more successful madams are easily identifiable around the capital, a visual testament to the fact that in Edo state, having money trumps the stigma of how it may have been earned.

Faith, a 24-year-old from Benin City, went to Moscow in 2013 knowing she would be working as a prostitute, just as her madam had done years before. What her madam didn’t tell her was that the debt she would have to pay—56,000—was in dollars, not Nigerian currency, which would have amounted to just $350.

After four years Faith managed to pay off her debt, but decided to return home to Nigeria last year when she accidentally became pregnant. It is still a source of shame to her family that she came back empty handed. “My father was not happy,” she says bitterly. “His expectation was that I would stay there as a prostitute so I could send home big money and get a big apartment for him.” The mother of Faith’s madam still lives in the same village, her luxurious home a constant reminder of how Faith has failed her family.

Florence, 24, about 10 days after getting married in Benin City on March 26. She jokes that she would love to have a house and a car—like the one in the poster behind her—once her hair salon business takes off. Lynsey Addario—Verbatim for TIME

Bringing perpetrators to justice remains unusually difficult. Not only are the young women committed to paying their debts, the oath forbids them from betraying their traffickers even when they are caught by law enforcement, whether it be European or Nigerian. Although Nigeria is one of the major sources of sex trafficking victims in Europe, NAPTIP has only been able to successfully prosecute 338 traffickers out of several thousands of arrests over the past 15 years, largely because victims rarely come forward and often refuse to testify.

Kara, the sex trafficking expert, recalls observing the trial of a human trafficking suspect in Torino several years ago, when one of her victims was called to the witness box. The witness, he says, “went into a fit. She couldn’t do it. She couldn’t talk about it. She was just in complete terror.” The case was unable to proceed, for lack of testimony.

Frustrated with her inability to prosecute traffickers in Nigeria, NAPTIP’S Director General Julie Okah-Donli asked for an audience with the Oba to discuss the issue of the oaths. Though the organization had arrested several of the priests, and used them as prosecution witnesses in court, national laws against trafficking were not enough to stop the trade. “This is a case where we need stronger intervention,” she says. “Because when the Oba speaks, the whole town shakes.” Now that more women are free to testify against their abusers, she expects the number of successful convictions to go up.

With the juju oaths in place, few traffickers needed to resort to the usual tactics of intimidation, corruption and threats that enable the trade to flourish in other countries. That is now likely to change. Already NAPTIP’s office in Benin City says it is seeing cases of intimidation and beatings against women who refuse to pay off their debts, and threats against those who have been asked to testify.

It also overlooks the fact that in many cases, parents and close relatives are implicated in the trafficking. “There will be more people willing to speak up,” because of the Oba’s pronouncement, says Edo State Attorney General Yinka Omorogbe, who heads up the anti-trafficking task force, “But it’s not so straight forward. You still don’t want to speak when the trafficker is your mother or father.”

Faith, 24, poses for a portrait in Benin City on March 25. She went to Moscow in 2013 knowing she would work as a prostitute but was unaware that the debt she would have to pay—56,000—was in dollars, not Nigerian currency, which would have amounted to just $350. Lynsey Addario—Verbatim for TIME

Okoduwa, who once traveled to Libya with the intention of making it to Europe, only to suffer for several years there as an indentured laborer, knows all too well that in most cases trafficking is just migration gone wrong. The Oba’s curse will likely make sex trafficking less lucrative and more risky, he says, but young Nigerians will continue to put their lives in the hands of unscrupulous human smugglers as long as they feel that there are not enough opportunities at home.

Wealth never made it back to Italy to pay down her debt. She was stopped in transit in Istanbul for having suspicious paperwork, and sent back to Nigeria. She doesn’t know what happened to her madam, and for the past several years has been haunted by the idea that her oath was still binding. The Oba’s counter curse, she says, has been a huge relief. She just wishes it had come earlier. “When I think of all the girls who have suffered, like me, to pay off debts that were cruel and unjust… a lot of girls went through hell. Our lives could have been so different.”

Faith, meanwhile, just laments the lost opportunities. If the Oba had annulled the oaths a few years earlier, she might have been able to return to her family in Nigeria with something to show for her suffering. “Maybe then I could have made money for myself in Moscow. Because I knew how by then.”

Roland Nwoha of Idia Renaissance, an NGO that helps victims of human trafficking reintegrate into Nigerian society through vocational training and small business grants, has already heard of several incidents where madams, fearful of the Oba’s curse, have freed their victims. But others have said that the Oba’s powers can’t reach Europe, and the oaths are still binding. The Oba is revered, and his curses are feared, says Nwoha, “But this is also a modern society. Do these things still apply? Unless we see something happen to those madams who insist on being paid, or on traffickers who defy the Oba’s curse, people might not take it seriously.”

A spectacular bolt of lightning on one of the well-known traffickers would be great, he says, half-joking, but a series of mysterious deaths, maybe a few heart attacks or a string of car accidents among recalcitrant madams and traffickers would make a significant impact. “So we are just waiting, two, three, maybe six months, for something to happen. But after six months, a year, if nothing happens….” He shakes his head. “Oh no, it will be bad. The traffickers will be even more powerful, because they will show that they are even stronger than the Oba’s curse.”

With reporting by Lynsey Addario and Bamidele Oni / Benin City and Olayinka Oluwakuse / Lagos

Contact us at letters@time.com.