Penny was almost 29 when she was trafficked from Rwanda to the UK, tricked into believing she could start a new life. Instead, she ended up trapped in a small flat in south-west London.
She had unwittingly stepped into a trap laid by a trafficker, becoming a commodity in what campaigners say is the world's fastest growing illegal trade - in people.
Yet when Penny agreed to meet the agent, introduced to her by a friend, she was unaware that human trafficking even existed.
"I didn't think about the consequences. I just took the opportunity to get out of the country," Penny said. Which countries are people trafficked from? "I had never heard what trafficking was all about until I was here. I didn't know anything about it at all."
Penny's story is just one of many that remain hidden. The UN estimates that some 2.5 million people are in forced labour at any given time, as a result of trafficking.
"We don't know much about the size of the iceberg that lies beneath," admitted Antonio Mario Costa, head of the United Nations Office on Drugs and Crime (UNODC).
"Like any other market - and it is a perverse kind of market - there is a supply in terms of people who are duped, coerced or tricked, and a demand, people who may be buying the sort of commodities we are talking about. And there is the act of connecting the supply and demand - those who do the trafficking," he said.
The UN says governments have fallen behind on commitments to tackle the problem and has called a conference in Vienna this week to urge more concerted action.
While 116 out of 192 UN member states have ratified an Anti-Trafficking Protocol, which came into force in 2005, some governments still do not have any legislation in place.
A few of the member states who have not yet even signed the convention include countries identified by UNODC as having a high number of people trafficked from them - such as India and Pakistan. Japan too, which scores "very high" as a destination country, has yet to sign the international accord.
Ruth Dearnley of the coalition of campaigning groups, Stop the Traffik, says human trafficking has never been a top priority for the international community.
"Enforcement agencies have always focused on the drugs and arms trade but this is the fastest growing global crime," she said. "If you make money out of illegal products then, in some ways, people are an easier product than drugs and arms."
Estimates - which are notoriously difficult to calculate - put the profits of the industry at $31.6bn (£16bn; 21.6bn euros) per year, making it the third largest shadow economy - after drugs and arms.
Penny was told the journey to the UK would set her back £1,000 pounds ($1,968; 1,347 euros).
But the fact that she didn't have the sum wasn't a problem. She was told she would be given both a place to stay and a job when she arrived, enabling her to pay the money back.
But the reality was very different.
"I ended up going with him to his place," she said. "I stayed with him that day. After four days he came on to me and started demanding sex. I refused, I didn't think that was the kind of deal I had with him."
"He forced himself on to me, started raping me. From that day, for about two weeks, it would just be daily." Soon, he brought men with him and Penny was forced to have sex with them too.
Once, she tried to escape, but he tracked her down and beat her badly, locking her in the flat. By the end, she remembers: "I was under his control - mentally, physically, I was under his control. I couldn't even sneeze without him knowing."
Even once someone has managed to escape the traffickers' trap, British campaigners say authorities are far more concerned about their status as an illegal immigrant, than as a trafficked person.
Penny, for example - repeatedly imprisoned for not having the right paperwork - is convinced the man who trafficked her is still plying his trade, unmolested by the authorities. "The policeman said, 'It's not him, it's you we have to deal with,'" she said. "I told them his address. They had everything. They weren't interested."
Crystal Amiss, of London's Black Women's Rape Action Project, said that frequently women's accounts of being trafficked are ignored when they emerge from the underworld and seek asylum.
"The priority is to stop people coming into the country. They are determined to have robust immigration controls and it is very easy to target people who have to work clandestinely," she said.
It is not just the sex industry that is fed by traffickers, though the UN estimates that 43% of those trafficked are used for forced commercial sexual exploitation. Workers are also exploited in the international textile, food and drink industries, often in the developing world, Mr Costa says.
Campaigners say, for example, that an estimated 12,000 children are still employed in the Ivory Coast's cocoa plantations. Hundreds are sold by their parents to work underwater for fishermen on Ghana's Lake Volta, where their nimble fingers untangle trapped nets.
The final and common link at the end of a long and complex chain, Mr Costa says, is exploitation.
"What counts mostly is the exploitation that takes place at several points along the chain as the human trafficking takes place and that is repetitive and prolonged. That is where most of the violence takes place."
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