Since publishing his first book, Old Friends, the start of his Chase Investigation series featuring private eyes in Auckland, he has written another 21 books. All are available on Kindle and have a hardcore following overseas, especially in the United States, which makes up about 75 per cent of his readership.
Best-selling UK author Peter James has even praised his novels for their "complex, believable police characters, strong tension, fast pace and the true ring of authenticity".
And although his identity is a closely guarded secret, some of his colleagues know his dark, literary secret.
"I don't broadcast it much but the ones who know are generally very supportive, and have even read some of them and given me feedback which is pretty cool," he says.
"Nobody has told me off for getting things wrong or portraying police in a negative light, which I'm quite careful about.
"I'm not here to take pot-shots at the department. You could do a warts and all thing but that's not my bag at all."
He's careful to avoid portraying real events or people but accepts he can't escape the "flavour of experience" when he sits down to write.
"Things like the language, the settings, the types of people… that's what you know," says McLean, who is also a big fan of US crime authors Ace Atkins, Dennis Lehane, and Vince Flynn.
"You can pretend to a degree, because it is fiction, but it's hard to get away from the reality because you know, for example, what a gang member is going to be like to deal with, you know what a grieving widow is going to be like, and you write it and it comes naturally.
"You have to reflect on things you've dealt with and the people you've met but then reframe the incident, or change the person enough that you're writing about something different, just with a flavour of your experience."
However, he tends to avoid "gratuitous or gruesome" violence and leans toward entertainment fiction.
Much of the violent crime he witnesses in his day-job is "a helluva lot worse that what the public realises".
"It doesn't always have to be dark, violent, dreary and life-changing with murders and child abuse," he says.
"There is a place for that, but there's also a place for escapist fiction where you could actually imagine yourself or someone you know doing that."
As well as his spy and crime books, he's also written three post-apocalyptic tales as part of his Early Warning series, which started before Covid-19.
They have since become "pretty relevant" and very popular, he says, and features an aspect of writing that he particular enjoys.
"I like seeing normal people stuck in really crappy situations and how they react," he says.
He's currently writing a World War II adventure story involving two Special Operations Executive agents – a toff English RAF pilot and a rugged, hard-bitten Kiwi soldier inspired by double-VC winner Charles Upham – on a death-wish mission behind enemy lines.
It's an action-packed "tip of the hat" to a generation he greatly admires.
And he likes writing about things he enjoys.
"I've never written to market. I write what I like. For instance, I could never write a romance – I don't know anything about it."
