One trick Austin uses is to finish each day with half a sentence, and complete it the next morning. He writes at his home office in Bombay, with views as far as the Waitakere Ranges; his thoughts outpacing his hand. Life is happier now thanks to a positive new mind-set and partner, artist Sallie Clough, who's a big supporter of his new career (that's her artwork on the cover).
"One of the happy by-products of writing is looking back at my past and considering those experiences - learning from them and, hopefully, doing things better in the future," he says. "These days I just try to be the best version of myself every day; a better partner, writer and father."
But Austin's police smarts are still very much with him. He sneak-read my list of questions before I asked them and has the steely bearing of a man who's used to being in charge.
"Could I have written these books without being a policeman?" he asks reading upside-down off my notepad. "The answer is no. The police work I did was great training for being a writer - giving evidence in court, writing reports and statements - and I have used all of that experience."
Austin's years working undercover figure in The Agency, too. He once disguised himself as a deaf priest and eavesdropped on a suspect on a train (in the book version he plays pool with the suspect).
Although he may have come late to crime fiction, he wants to be up there with the genre's heavy-hitters.
"I respect writers like Paul Cleave, Ian Rankin and Lee Child, but I don't want to emulate them," he says. "They've got a formula that works extremely well for them. I don't pretend I can do what they do, but then I like to think they can't do what I can either."
After a rocky road to publication - a dodgy local agent who sold the rights to an equally dodgy American publisher - ("I didn't do due diligence," Austin says, clearly annoyed at himself) - he has since bought back the rights to The Agency.
The good news is that book quickly sold out after its first printing - quite a feat for a self-published book - and is now on its third.
"I think it's only a matter of time until the momentum reaches a tipping point," says Austin who's been invited to attend a crime writer's conference in Scotland next month off the back of the novel's success.
"As I write more I gain confidence. I think it's key to surround yourself with the best people - Stephen Stratford edited The Agency and we have a great team who are the very best at what they do."
He wants the series to find a home at a top international publishing house.
The next outing for Calder (who faced a wily female serial killer in The Agency) is the intriguingly titled The Second Grave - from the Confucius saying - "Before you embark on a journey of revenge, dig two graves." Calder returns to England and comes face-to-face with his old nemesis in the police.
"This has a proper villain in it - one who's a really nasty piece of work."
For Austin, it seems, crime writing may be the best revenge of all.
The Agency (Nationwide Book Distributors, $30)
by Ian Austin