The Sisters Brothers, By Patrick deWitt

'Bring me the head of Kermit Warm'

Turning the final page of The Sisters Brothers, the second novel by the Canadian-born writer Patrick deWitt, the reader comes face-to-face with a mug shot of the author, an angular-jawed young man wearing a deadpan expression.

So this was him, then. He was the creator of this unsettling, compelling and deeply strange picaresque novel.

The Sisters Brothers is one of those books that they call "genre bending". The story, set against the backdrop of the 1850s Californian gold rush, goes something like this: two gun-toting brothers, Eli and Charlie Sisters, are instructed by their boss, the shadowy "Commodore", to hunt down and kill a chap by the unlikely name of Hermann Kermit Warm. They embark on a thrills-and-spills adventure across California, encountering a quasi-Beckettian "gallery of moribunds" on the way. The dénouement is at once serendipitous and circular.

Cowboys are richly represented in American fiction. The obvious writer to mention is Annie Proulx, author of (among many other things) Brokeback Mountain. It's safe to say that DeWitt is not very like her. Whereas Proulx looks for the particular, the nuts and bolts of life, DeWitt is concerned with driving narrative, violence and (above all) the fraternal relationship. Another obvious writer is Thomas McGuane; DeWitt is absolutely nothing like him. McGuane uses the genre to explore the everyday anxieties of American life, but DeWitt is concerned with the immutable characteristics of human nature. He's also not impartial to the odd flurry of magic realism.

As Eli and Charlie encounter one bizarre situation after another – a perpetually weeping man, a young girl intent on poisoning a dog, a gaggle of "painted whores, seven in number, each of them in frills and lace" – I find myself thinking of Henry Fielding's Joseph Andrews. The madder vignettes (a mud-drinking tea party) even evoked shades of Alice in Wonderland.

But for all its wry playfulness, The Sisters Brothers is no comedy. The travails of the humane yet morally ambiguous protagonist in a hostile, lawless and unpredictable universe have echoes of Cormac McCarthy's speculative classic The Road. That book imagines a journey through a world in which civilisation has died; this book explores a world in which civilisation, as we know it, has not yet emerged. But both have much to say about the business of being human.

The narrative, written in the voice of Eli, captures perfectly the mixture of rivalry, admiration, love and disdain that makes up the lot of the younger brother. When he is bitten by a spider and wakes up with a horribly swollen face, his big brother says that he "looked like a half dog, and tossed a stick to see if I would chase it". Yet when Charlie suffers an accident, Eli cares for him devotedly. It is this poignant observation of brother-ness that makes me glad to have gone on this journey, even if I'm not sure exactly where I ended up.