This is a set of beautifully crafted short stories, with unforgettable characters, each of which stands entirely on its own as a little peek into humanity. It also works as a raw exploration of the reverberating impacts of violence, and specifically, of the actions of Ivan Milat, whose violence, arrest and conviction were a seismic event in Australian culture.
This is fiction, the chronologies have been changed*. The title inverts the highway numbers from the Hume (M31) in a winking nod that this is a mirror version, an imagining. Milat's doppelganger Joe Biga is not Milat. Nor does the killer ever assume center stage.  Some of Macfarlane's stories examine those on the periphery of his violence - the police officer who worked on his arrest; his wife's family, his mother, his neighbours, a brother still haunted by his disappeared sibling and a teenage girl who will grow up to escape him. The stories are set in different times. In three of these, where we meet characters with the violence still in their futures, the stories function as almost entirely stand alone adventures. It is only through our knowledge of the anthology, subtle connections between the stories - a name dropped here, a date there - that the darkness shades the story. In probably my favourite story Hostess, a twist ending provides the "this is what was going on all along" moment, but of course we know that this isn't the real reveal at all. It should be pointed out that while some of these characters share superficial similarities with the Milat case, they are not those people. These are fully imagined and realised characters, with engaging inner lives. In Demolition, for example, Biga's next door neighbour tries to fend off a journalist on the day 'his house' is being demolished, but is consumed with regret and longing for the lover who lived there when they were young. 
But other stories focus on those swept up in the cultural moment - true crime podcasters; rubberneckers, the actor who uses the telemovie to gain career gravitas and in the 1990s, a young women terrified her boyfriend is secretly the killer. Some of these - including a politician who shares Biga's name morosely cooking sausages on an election day he knows will not be his - are played partly for laughs, but never without realism (well, except for the pollie cooking sausages which is not how Democracy Sausage works at all, that annoyed me). There is snark at the edges of some, especially the very American podcast story, one about a big-city couple who dine out on their stories of meeting one of the victims (and the couple who in turn dine out on knowing them) and Tourists, about the rubbernecking impulse - but it always weighted, these characters don't like parts of themselves and juggle their empathy with their own sense of drama and importance. The only story I could not bear was Abroad, which includes a ghost story told at Halloween and I will confess to skimming past the story, knowing that the macabre-for-thrills was more than I could cope with in the face of the all-too-real horror I know of from the Milat case. McFarlane utilises our own knowledge to bring the dark, she does not put it on the page. (This has led, I found, to some interesting reviews from the US release of the book, where the case is not well known, and the book reads with less gravitas - it holds up).
There are other themes present through the stories. There is an enduring theme of restlessness, of characters perpetually on the move. Travel anecdotes abound, and at the other end of the scale, locals defend their turf - two older women grump at new arrivals at their open air Sydney baths (this is a real thing);  the locals cold-shoulder the new arrival at work. As someone who came of age during the era of the 'backpacker' murders, it felt as if McFarlane's themes paid tribute to the backpackers themselves. The book also explores the way we create and tell stories - how these shape our individual and collective realities.
As you can tell if you have read this far - I liked this rather a lot. I will be rather shattered if it doesn't appear on the awards circuit. McFarlane's books just keep getting better, and I really think this is a book which should be part of our national canon. Great literature helps us to understand who we are and who we have been, and there are few books which have captured the scope of Australia in the way that this one does.

*It did unreasonably distract me that Biga was born in the 1960s, a good 20 years younger than Milat, but described as being old at his death when he must have been in his 50s. I have struggled to let this go. I will get there.