Federal investigator Aaron Falk drives into South Australia's vibrant, verdant wine country to begin a week's vacation with friends at a vineyard. Instead of police duties he has godfather responsibilities, attending the christening of Greg and Rita Raco's son, Henry.

The ceremony was due to go ahead the year before and Falk made the trip to Marralee for it. However, a tragedy derailed the event. On a warm spring night at the Marralee Valley Annual Food and Wine Festival, 39-year-old mother Kim Gillespie, a member of the extended Raco family, abandoned her 6-week-old daughter in a stroller. She then vanished and hasn't reappeared.

Now, one year on, Kim's absence is still keenly felt. Despite the fact that one of Kim's shoes was found in a nearby reservoir, her teenage daughter Zara refuses to believe the worst and insists she has spotted her mother several times over the past 12 months. And for all of Kim's mental health problems, Greg Raco cannot imagine her turning her back on her newborn.

Falk joins the family at the festival as they distribute missing-person leaflets in a bid to jog memories and retrace steps. Zara appeals to the crowd from the main stage: "Someone here tonight knows something."

Soon Falk and Raco can't help themselves and start to make inquiries. Another cold case presents itself, one involving a hit-and-run fatality six years ago, also down by the reservoir and also at the opening of the festival. A typical small-town coincidence? More oddities raise further questions. Why did none of Kim's family or friends admit to having a conversation with her at the festival? What happened to Kim 25 years ago at a bushland party near the reservoir?

Meanwhile, as Falk falls deeper for Gemma, the festival director, he finds himself forced to answer a different kind of question. She doesn't want an "interstate romance" made up of "snatched weekends and champagne and sunsets." Should he then quit his job, uproot from Melbourne and move down here to make their relationship work?

"Exiles" marks the third and, supposedly, final outing for Falk. Once again, Jane Harper triumphs with an intelligent, beautifully crafted crime novel, one that is more of a slow-burn mystery than a high-octane thriller, and all the better for it. Falk remains a quirk-free yet quietly compelling creation whose great methodical mind ("Rule it in until I can rule it out") won't rest until it irons out incongruities and pins down culprits.

Harper's characters, old friends with individual secrets in a close-knit community, are masterfully rendered. Her landscape is, as ever, no mere backdrop but rather a vivid panorama central to the drama.

As the book reaches a hugely satisfying conclusion, Falk comes to learn "What people will do for someone they love." "Exiles" may well prove to be Falk's swan song, but Harper leaves her readers with the faint yet very real hope that we haven't seen the last of him.

Malcolm Forbes has written for the Times Literary Supplement, the Economist and the Wall Street Journal. He lives in Edinburgh, Scotland.

Exiles

By: Jane Harper

Publisher: Flatiron Books, 368 pages, $27.99.