I can see how this got into the Man Booker Prize shortlist. A dreamy cowboy crime caper cum philosophical rumination on the criminal mind would be the pseudo-intellectual way of putting it. In plain language this is a damn good, deceptively simple read. 
 Two hired killers; the Sisters brothers (yes, their last name is Sisters, see what he did there) work for a shady crime lord known as the Commodore during the California gold rush. They are on the trail of a certain Herman Warm, said to have stolen something from the Commodore. They must kill Warm and steal his 'formula'. This 'formula' is in the thick of the plot here. 
 But Warm is not what the brothers expected, and they find themselves in somewhat of a post coming-of-age coming-of-age when they are forced to review their lives and evaluate just how they ended up being violent hired guns. The younger brother Eli, through whom the story is narrated, is an extremely well constructed character. Ostensibly insecure and dim, yet surprisingly capable of deep insight only to which the reader is usually partial to. 
 The book might get a little slow sometimes but that's ok, its capable of being ingested slowly. Like you can easily catch up with it again after a period of not reading it. 
 Some money quotes: 
 Eli, about to shoot a man: "My very center was beginning to expand, as it always did before violence, a toppled pot of black ink covering the frame of my mind, its contents ceaseless, unaccountably limitless. My flesh and scalp started to ring and tingle and I became someone other than myself, or I became my second self, and this person was highly pleased to be stepping from the murk and into the living world where he might do just as he wished. I felt at once both lust and disgrace and wondered, Why do I relish this reversal to animal?" 
 Eli, feeling dejected. "I entered a modest restaurant and took a seat by the window, watching my hands on the bare table. They were still and ivory looking in the light of the planets, and I felt no particular personal attachment to them."