Such quick success can raise the spectre of the dreaded "difficult second novel", but Sanders says he found writing By Any Means - released yesterday - smoother and more enjoyable than his début. "The thing about being an unpublished writer is that, chances are, nothing is going to come of your efforts," he says. "Whereas with By Any Means I found it a lot easier because I was familiar with the characters and I was working towards a specific goal - I had a contract for that book."
Not that the process was completely without missteps; Sanders initially toyed with extensive plot outlines, a shift from the free-flowing approach he took with his debut and two unpublished novels written as a teenager. But he found he didn't stick to what he'd outlined, and quickly returned to his natural tendency for a "vague idea of an outline", and chapters evolving from the preceding chapter.
"I think with each book that I've written, whether it's been published or not, I've seen a definite step up, whether in terms of story or quality of writing."
It's easy to forget how young Sanders is. There's a maturity to his answers and outlook that bring the phrase "old head on young shoulders" to mind. While his publishing career celebrates its first birthday this month, Sanders has been writing novels for several years.
"I started writing crime as a result of the interest I had in reading it," he says. "The first thriller I read was The Day of the Jackal, by Frederick Forsyth, which I came across at intermediate school. I absolutely loved it. It exposed me to the whole world of crime and thrillers, and led on to the likes of Michael Connelly, Lee Child, Peter Dexter and James Ellroy. [Then] when I was in the sixth form I had a crack at writing my own novel."
That first effort resides in a shoebox under his bed, never to see the light of day. But the learning experience was invaluable, says Sanders. "The value of finishing something, and also just trying to be aware of all the different elements that make up a story. Stories don't just rest on plot, they don't just rest on character, they don't just rest on setting. You have to have an understanding of how all three interact. And I think it's one of the reasons why people who are just starting out go off the rails."
He laughs now about the "off the rails" aspects of his own first effort, set in Los Angeles because that's where 16-year-old Sanders thought good crime fiction was set, and his private eye Alex Denver was "conceived arbitrarily".
By the time he wrote The Fallen, he'd "thought a lot more" about developing a main character, rather than "just picking random characteristics out of a hat and lumping them together".
With Devereaux, Sanders considered everything - from his background, to where he lives, the car he drives, the music he listens to, the actions he takes, and his outlook on life - not as mere details in a character sketch, but as meaningful evidence that says something more about the reclusive, rebellious cop. That gives readers insights into who he is.
"I wanted a character I was interested in." Location was another key evolution for Sanders. He realised that just because Auckland-set crime fiction wasn't common, it didn't mean his hometown couldn't be a rich setting for the type of novels he wanted to write. Knowing the city well meant he could create a far richer sense of place - an important aspect for contemporary crime novels - than by trying to mimic others' evocations of traditional hotspots like Los Angeles.
Sanders could describe things as a local, and give a real sense of how they "felt", not just looked.
"I don't particularly see Auckland as a place riddled with crime," he says, "but I found it an interesting place where you could conceivably set a crime story and have people believe it."
By Any Means (HarperCollins $24.99) is out now.
