It started with two 6-year-old girls and this promise: "For thirty US dollars, you can do whatever you want to these girls for one hour."
That was 2002, and when he heard those words, Daniel Walker, of Christchurch, was thrilled, but not for the reason you might expect.
Walker was an investigator working undercover in the sex trafficking industry, and he knew that thanks to his hidden camera, he'd just secured enough evidence to convict a pimp.
It broke him in the end though, the undercover work.
His marriage, his moral compass, both gone. And it ended in the worst possible fashion.
"She was 29-years-old. She had been trafficked some years earlier. Paid off debt, came back to make money. She had a tragic story and that vulnerability I responded to at some level, and a whole lot of other factors. I was in the state I was in and she was quite aggressive I suppose. I said no, but didn't."
After four years in which Walker admits he'd been in more brothels than most men have had hot dinners, he cracked.
"I'd become so desensitised that I crossed the line. In the space of a few seconds, I betrayed everything I believed in. I betrayed my wife, my vows, just like that and I couldn't believe it had happened."
He had slept with a prostitute he had tried to save from prostitution.
Talking to Walker now, it's clear the heavy toll the work has taken on him. On returning to New Zealand, Walker, a police detective, spoke to a psychiatrist who recommended he write about his experiences, a cathartic process which resulted in his book, God in a Brothel.
He said he revealed the details of his fall from grace for a number of reasons. He said he realised that for his recovery, he had to forgive himself. Also, through the book and the anti-sex trafficking non-governmental organisation he now runs, NVader, he wants to make best practice advice available for other groups tackling the scourge of modern day sex slavery.
When he started, he said, there was no guide book. Across four years and 12 countries, he has tackled what is becoming the No 1 global criminal enterprise.
He said that right now - today - there are more people in various forms of slavery than ever before. Estimates suggest more than 27 million people are held in some form of slavery, two million of those in the sex trade.
And it's easy to see why, he said.
The conviction rate for sex trafficking is pitifully low for a start. Then there's the money. Cocaine, heroin, cannabis - they can only be used once, while the horrific reality is a women or child - male of female - can be raped again and again.
Over his four years of undercover work, Walker said he rescued hundreds of victims and helped prosecute dozens of traffickers and pimps, but the seeds of his downfall were sown in the methods required for the work.
"Living in this world that is so foreign where, essentially to be successful, you have to adopt many of the attitudes of the people you're emulating, and then come back and try to be an emotionally available and loving husband. Over time it destroyed me."
The work was dangerous too.
He recalls one brothel where, despite gaining the trust of the majority of the pimps, one remained suspicious.
He demanded Walker have sex with a 5-year-old girl. When he declined, "he leaned over and said if you come back here, I'll kill you".
It was a serious threat, too, he said, as the country in question had undergone civil strife "and pretty much everyone had an AK47".
Incredibly, he was able to take a positive from this encounter.
He said the man asked him directly whether he worked for an NGO. The reason? They are feared by these men as unlike local law enforcement, they can't be bribed.
Corruption, unfortunately, goes hand in hand with sexual slavery.
Walker tells me about a girl called Maria who managed to escape the brothel she was kept in, only to be returned by the very police she had sought sanctuary from as they were the trafficker's protection, paid for by cash and sex.
This corruption touches on the story he says haunts him most to this day. He said he had returned to a brothel where earlier the children had pleaded for rescue, only to find they had all vanished, thanks he believes to a tip-off from a corrupt policeman.
In many cases he said, "it's not one or two corrupt officers, it's a corrupt system."
Even this isn't without some hope though. He recalls one corrupt officer he encountered who was in the pay of the local drugs trade. The man was also a father to two daughters however, and helped Walker secure prosecutions.
There are other factors that support the trade in human beings; open borders, poverty, the commoditisation of sex, and sometimes local culture.
Walker said in some places, women were simply not valued and their slave masters can be family members.
For many though, and this is what he found hardest to comprehend, "they just want a TV set".
Through this interview, and his book, Walker is eager to make one point very clear amid the horror of what he has seen, and that's the hope.
Famed abolitionist William Wilberforce, he said, was told the African slave trade couldn't be dismantled.
He said that empowering local agencies, through NGOs such as NVader, and educating men means this modern slavery can be beaten.
And he's crystal clear it is slavery. "We're not fighting prostitution. We're fighting slavery."
Walker's book can be found on Amazon, Whitcoulls online and Manna Christian Stores. More information on the work of NVader can be found online at nvader.org.
- © Fairfax NZ News
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