Mark van Leewarden details his fascinating and sometimes unsettling true-life story as a former undercover cop in his memoir, Crimetime: From Undercover Cop to International Investigator.
He was a member of Auckland’s criminal underbelly for a year, gathering intelligence and trying not to get found out or worse.
Van Leewarden not only survived to tell the tale of his double life, but he went on to become New Zealand’s most successful international fraud investigator.
After being in the force for 15 months, 20-year-old van Leeward was offered the chance to go undercover into New Zealand's criminal underworld in the 1970s.
"I was sort of, I suppose, getting slightly tired of being in uniform," he tells Kathryn Ryan. "I don't know whether the bosses picked that up or the fact my shirt was always hanging out of my uniform when I was walking the beat.
"The thing is that at that age, you're risk modulator is not that good, and it really is impossibly uninformed consent ... not that you know it at the time, it's almost like playing Russian roulette with your personality."
His undercover backstory was that he was a 'rich trust kid' who had gone off the tracks.
Starting with being a "fence" (a seller of stolen property), he went on to deal with the drug guys at night clubs and within three weeks met a major crime figure who introduced him to other targets, he says.
"I had one primary, and then another Black Power associate who I ran with as well, we spent a lot of time together.
"You were acting and living as a criminal and over time, even though you don't see it yourself, you start to adopt a criminal persona.
"Once or twice, you're gonna go and meet up with your family and they'll see the deterioration. But you don't really notice it because you necessarily have to act like that to survive."
He gained the trust of Auckland crime boss Ricki Goodin but his girlfriend became dubious, van Leewarden says.
"There might be a lot of bravado about criminals in the scene, but the reality is that their women are very influential, so you had to tiptoe around those relationships."
But one day, things came to a head and Goodin ended up stabbing his girlfriend to death, he says.
"I was obviously a police officer, so I put all the evidence together in terms of being able to secure the [murder] conviction.
"But as a result of that, I was named as a nark obviously on the street, so there was a contract put on me come as a result of being either seen as a nark or an undercover.
"And so there had to be a decision made then as to whether I was going to go back into the scene, knowing that I was going to be approached. And my [operator] said 'look you have to go back 'cause if you don't go back in, it's going to reaffirm the thoughts that you actually are a nark'.
"So, in a very difficult situation, I went back into the Schooner [Tavern], into the very guys that were gonna take out the contract on me [while] every fibre of my being was saying 'don't do that'."
But once the end of his operation came, it was difficult because he'd made connections with people, including one woman who appeared to have fallen for him, he says.
"I remember on that termination day, I was starting to wonder in what world I actually sat, was I stuck somewhere in the middle between a criminal and a police officer?"
To get back into his headspace, he went took to the South Island to be alone for six months, he says.
"It's a difficult time because you know that your personality has changed and you can't get that back again, so you need to try and take the best that you can out of what you've done.
"You jump from 20 [years old] to 30 I suppose in terms of your experience ... 10 years [of your life] evaporate ... probably some of the more easy going type attributes go, you know, trusting and having faith in people I suppose."
He now uses his experiences in the civilian world, being a barrister specialising in international fraud investigations and is also the managing director of a private investigation and security company.
He says he feels satisfied about being able to do things like return money from the jaws of Russian mafia to the likes of retirees.
"The biggest worry doing that sort of work [was] that your family were potentially in jeopardy.
"Because if you're operating against international organised crime and you're freezing bank accounts and creating legal issues for them, then you become a target."
In one incident, they'd tracked down $20 million stolen from a Swiss bank to a man in Malaysia, he says, and an arrangement to meet was set up.
"We got contacted by the FBI who said that they had credible intelligence that the Japanese yakuza would detonate a device in the hotel room to try and kill the guy that we were talking to because, unknown to us, he already had ripped them off before.
"It wasn't hard to decide not to go to the meeting the next day, that's for sure."
Several years ago, writer Alan Duff approached van Leewarden about writing a novel based on his adventures, but he found it would be better for van Leewarden to write his own story.
He says he has no regrets, but had to face up to his past while writing the book.
"It was quite difficult to confront ... in terms of some of the things that I'd done, but over time it actually became cathartic and it sort of helped me."