The road to Bangkok's party district is paved with bad intentions. Happy-headed Western tourists are drenched in sweat and soaked in booze. Garish neon lights and flashing signs lead them towards bars and brothels.
As dusk approaches, pounding bass music spills out of the clubs, along with packs of young girls wearing bikinis and heels.
The smell of Thai food wafts through the market, as kids dart between the stalls, trying to pry coins from the pockets of wide-eyed visitors. The place offers an intoxicating feast for the senses.
"Bro, I love it here," says 27-year-old Matt Anderson, in a soft Aussie drawl. "There are no rules in Thailand. I work for a logistics company, so I spend a lot of time travelling. I work hard, but I also like to play hard, you know?
My job's stressful, so I get out at night and enjoy myself. And everything's so cheap here. Beautiful girls everywhere. The beaches are great. You can drive a 1000cc motorbike. Seriously, man, what more could you want?"
Matt takes a sip of lukewarm local beer, and scans the bar he's standing in. It's small and narrow, with a concrete floor. Down one side, there's a stage, where four girls cling to poles while dancing to house music. On the other side, a row of velvet seats surrounded by mirrors. For many guys, this would seem like paradise.
But if Matt's lifestyle sounds too good to be true, that's because it isn't real. He's not Australian. He's not a businessman. And his name isn't even "Matt". The truth: he's a 27-year-old Kiwi named JD Koppel, an undercover agent on the hunt for child sex traffickers.
"As soon as I arrived at the bar, a pimp was all over me," JD recalls. "He wanted to buy me a drink. He said 'What do you like? I'll guarantee I can get it for you.'
I told him I was keen on very young girls. He said he could get one for me. Her name was Mei, and she was 14 years old. The pimp called her over. She was pretty shy, and sat next to me nervously with her arms folded. We began to talk."
JD spent weeks gaining the trust of Mei and her pimp, who was a smart man with a fearsome reputation. He recorded all of their conversations on hidden camera. After a few weeks, he and his colleagues were ready to conduct a sting on the brothel.
But when he arrived, JD found the place was quiet. Only a handful of young girls were there, and they were fully dressed. He learned that corrupt cops had tipped off the bar manager about the covert operation. When JD asked where Mei was, the pimp was anxious and shifty.
"He whispered to me, 'You can't take her to the hotel. Not tonight. They're coming to raid this place.' I was playing a role, so I had to put on my surprised face, and pretend I was shocked. But inside, my heart sank.
I was so incredibly angry that the details of our operation had been leaked. Usually when that happens, the bar owner will take the kids out and ship them to another region. I didn't know if we would ever find Mei again."
Into dark places
JD Koppel can pinpoint the moment his life was flipped upside down. Four years ago, he was working as a landscape designer in Auckland, when he stumbled across a website for Destiny Rescue.
The charity was founded by Kiwi-born Tony Kirwan, a humble electrician who quit his job and moved his family to Thailand to create a rescue organisation. After hearing Tony's story, and paying him a visit, JD decided to join him.
He isn't the only young Kiwi to make that bold move. Two years ago, Jerram Watts had a "pretty perfect" life in Wellington. It included a girlfriend, great flatmates and a coveted job as a reporter on 3 News.
But even when the cameras were rolling, he felt like there was something missing. He'd been watching his old schoolmate, JD, build a new life in Thailand, so he decided to join him.
"Seeing JD's passion made me jealous," he says, "but in this line of work, you can't have a hero complex. Some people want to do this work because they want to be like Liam Neeson in Taken. Actually, we aren't looking for adrenalin junkies.
We need men whose hearts break for these girls. We're after humble guys with strong convictions. You need to be mentally tough and emotionally stable. If you don't know who you are and what you believe, then when you enter these dark places, you're going to be hit for six."
The brutal truth is that many of Bangkok's working girls were sold into slavery by their own parents, who wanted them to earn money to pay for food and shelter or, in some cases, gold necklaces and skin whitening creams. Other families were conned by traffickers, who claimed they were hiring teen girls to work in the big city as waitresses or cleaners.
Before Destiny tries to rescue a girl, the agents need evidence of her age, and proof that she's being exploited. Often, they can help a girl to walk out of a brothel without much hassle. But other operations are expensive and dangerous.
They take place in countries like Cambodia, Burma and Mozambique; places where JD has been groped by pimps and been threatened with weapons by bar owners. In some situations, he faces the prospect of being kidnapped.
But his main priority is to ensure the safety of the child he's trying to rescue. Usually, the girl can't wait to get out. Sometimes, however, she'll turn down an offer of freedom.
"One night," Jerram says, "we were talking to a 15-year-old girl. I said, 'Is this really what you want to be doing? Surely you have dreams? There must be things you want to do with your life'. She said, 'Don't tease me'.
I told her we could get her out of there, and give her a new life. She looked at the translator, slapped him in the face, and told us to take her back to her pimp. We walked out of that place, and I felt like I'd failed. But I had to remember that the last time a man promised her a new life, she ended up as a sex slave.
"So I took her back to the brothel. She got off the back of my scooter in a dark, dirty carpark. I called after her.
She came back and gave me a hug. I said, 'I hope I see you again'. She walked off into the darkness, and that's the last I ever saw of her. I just went back to my hotel room and cried, and cried and cried."
Hope among the heartbreak
The fruits of this heart-wrenching labour can be found in Chiang Rai, an idyllic rural town in northern Thailand. It's a town of rice paddies, jungles, hills - and hope. Here, Destiny has one of many 'rescue homes' where former child sex workers are given counselling, healthcare and education.
There's vocational training, like screen-printing and jewellery-making. Some girls head off to uni, or choose to work at Destiny's own café. They learn life skills, and they learn how to laugh again.
It's a tough transition. Some girls resort to their old survival tactics: lying, stealing and manipulating. Others run away, or even try to commit suicide. On top of their trauma, they're handling the same fears, hopes and desires as any other teen girl. Jerram says they require "grace, love and patience" as they begin to heal. The girls are encouraged by Destiny's staff, who treat them as part of a big family.
"I decided to make a new start for my life," says Dao, who had spent nine months in a brothel. "After I came to live in the home, my life became so much better. Now I'm very happy. I have learnt how to look after my money and I really enjoy all the fun activities we can do. Someday I would like to have a beauty salon."
Stories like Dao's are now creating a ripple effect, far from the hustle and bustle of Bangkok. Back in Auckland, 23-year-old personal trainer Dean Shippey has started 'Find Her Smile', a youth movement aiming to raise awareness about sex trafficking. He's spoken in schools and churches, where his words are often met with surprise and shock.
"We think trafficking isn't a big deal, because it seems so far away," he says. "But we need to educate ourselves. I have friends in Thailand at the moment, and I know what they're getting up to.
They're good guys, but when they walk into a bar they won't realise that those girls are not there by choice. If you told them, 'Did you know that girl's only 15?', they'd be out of there in a shot. But I don't want to put the blame on guys in my age group. I actually want them to realise the power they have to make good choices."
One day, Dean hopes to travel to Asia and follow in JD's footsteps. But in the meantime, he and his friends are happy to raise money for charities like Destiny Rescue and Tear Fund, which are working at the frontline.
"We had one guy run 5 miles a day for 30 days, and he raised a grand. We had a fundraising party. A couple of girls did a bake sale. There were kids coming up to me in church saying, 'I don't have much to give, but here are some coins'.
It was encouraging and heartbreaking at the same time, because this generation gets such a bad rap. People think we're lazy and self-centered. But young people want to find a revolution they can be part of."
The anti-trafficking "revolution" has consumed the lives of many undercover agents, leaving them burnt out and emotionally scarred. It has even cost their own relationships. But JD says he's in a healthy mental space.
He's happy to see a counsellor, to talk about what he's seen on the job. He and Jerram aren't paid for their work, because Destiny relies mainly on volunteers who're sponsored by friends and family. Both men say they're driven by their Christian faith.
For JD, however, it's time for a new season. He has taken a break from Destiny, and returned to Auckland to apply for Police College. He hopes to develop skills that will help him when he heads back to Asia in the future. Rescue work, he insists, will be his lifelong vocation. But for now, he can take a breath, and spend a few months living outside the shadows.
A life saved
Before JD came home, there was one thing on his mind: that failed sting in Bangkok. So, four months on, he returned to the bar, where the pimp - his old mate - had some very good news: he was back in business.
And this time, JD wouldn't waste any time in getting Mei out. His team planned a new operation for the very next night. They asked for help from a different branch of the police; a branch that was brave and trustworthy.
As dusk fell, JD and another agent headed to the bar, wired up with cameras and mics. He spoke to the pimp about how much he'd pay for Mei's services, and exactly what she would do for him. JD handed over a wad of cash - marked bills with serial numbers that could be tracked by the cops. He and Mei slipped out of the door and into the night.
"We headed for a hotel just up the road, which charges by the hour. There were undercover police along the route, tracking our movements. As we walked, Mei's attitude began to change. Until then, I'd been a friend to her, but now I'd bought her for sex. All that trust I'd built up was going down the drain.
She must have been thinking, 'This guy doesn't care. He's just like all the others'. That was hard, walking with a 14-year-old girl, past hundreds of eyes. All of them know what you're about to do. Some give you a smile and a wink. Guys from New Zealand and Australia say, 'Good on ya, mate! You've found yourself a good one!'"
They walked up a dark alley towards a side door, leading to an elevator, which took them up exactly three floors. JD led Mei into a room that was wired up with hidden cameras. She stood close to the door, as if she was hoping that somehow - against the odds - JD wouldn't want to have sex.
He told her to go and have a shower. While she was in the bathroom, JD sat down on the bed and pulled out his cellphone. When Mei came out of the bathroom, the cops were waiting for her.
JD had to stay in character, and pretend he had no idea what was going on. The officers said he was under arrest. JD protested. It's a necessary part of the act. As soon as JD had been taken out of the room, he and the other agent got into a cab and headed the airport.
At the very same movement, a separate police team was raiding the brothel that the girls had come from. They arrested the pimp, who now faces a lengthy court process.
"The biggest feeling is one of relief," says JD, "because so many things can still go wrong at the last minute. Until the end, there's so much adrenalin and emotion. And then suddenly you find yourself sitting in the back of a quiet taxi, thinking to yourself, 'Was that a dream? I mean, did that really just happen?'"
Mei is one of 1500 girls who've been pulled out of the sex industry by Destiny Rescue since 2011. She spent a month in a government-run welfare home, before being placed with trustworthy family members who were able to look after her. But even though he played a critical part in her rescue, JD didn't get to see Mei's new life.
He didn't get to see her smile. In fact, his last memory of her is from those blurry moments when the cops moved into that musty hotel room. If he closes his eyes, he can still see Mei's face, frozen with fear, disbelief and shame. As JD was dragged out of the room by the police, while staying in character, he whispered his final words to Mei: "I'm sorry".