Jake and Elwood Blues claimed to be on a mission from God, but Eli, the rugged road warrior whose destiny lies somewhere west of the Mississippi, really believes it. With the Lord as his shepherd and a King James Bible stashed next to his machete, Eli wanders America’s post-apocalyptic wasteland of the not-too-distant future with a singular purpose: spreading the good word.

It’s easier said than done. “Stay on the path,” Eli (Denzel Washington) mutters as he surveys the skeletal remains of a once-bustling nation, willing himself onward in a lonely journey made treacherous with pitfalls. Cannibals scour the countryside for easy prey, and, more ominously, there’s Carnegie, a power-hungry tyrant eager to make what’s left of the lower 48 his personal playground.

Carnegie (Gary Oldman) collects dilapidated real estate and ruthless thugs, but there’s one thing he doesn’t have – a Bible, the “weapon” he needs to hold sway over the hope-starved masses. He shrewdly regards the book not as a guide to salvation but as a shortcut to mind control, and so he sends his goons to find one.

But where? In the wake of some untold catastrophe, widely attributed to the failure of religion and God’s appalling indifference, Bibles have been banished from the land and destroyed. Eli’s copy is the last of its kind, making it a hot commodity to those old enough to appreciate the power of the gospels.

And yet how quickly people forget. Set just 30 years in the future, Book of Eli asks us to believe that the Bible, the most influential piece of literature in the history of Western civilization, has all but vanished from the public consciousness.

It’s a premise that strains the imagination, but accept it we must, as it sets up the inevitable showdown between the two men who do remember: Eli and Carnegie, the noble evangelical and the devil incarnate. Carnegie, who looks to his biography of Mussolini for life lessons, wants the book badly enough to kill for it. Eli, who rarely turns the other cheek, is similarly inclined.

If that makes Eli sound like a contradiction of sorts, he is. Book of Eli, the first feature from directors Albert and Allen Hughes (Menace II Society, From Hell) in nine years, strikes an uncertain balance between righteousness and rage, as its high-minded hero smites the mortal demons in his path without mercy. But it’s never boring, and thanks to Washington, neither is Eli.

I’m not sure how Eli’s closed-fisted approach will play with Christians raised to observe the Golden Rule, much less how to respond to a movie so humorless and grim. As violent, post-apocalyptic fantasies go, Book of Eli seems awfully familiar – it’s The Road with a heftier body count – but it’s diverting enough. In its attempts to find significance in Eli’s strange spiritual odyssey, though, it falls short.