The documentary Cartel Land is about the Mexican drug trade in the same way Moby Dick is about a fish — nominally, symbolically, as a single point of contact in a tale so monstrously bloated with violence, corruption and thwarted desire that it baffles comprehension at every turn. Just when you think you have a bead on this film, it wriggles free of easy assessment, turning morality inside-out to such an extent that life itself becomes a blur of guilt and complicity, every hand bloody.

With an almost inconceivable level of access to his subjects, embedded filmmaker Matthew Heineman captures the on-the-ground activities of two vigilante groups that rose up to combat the Knights Templar, a drug cartel based in the Mexican state of Michoacán and notorious for acts of medieval atrocity and terror.

On the U.S. side of the border, in Arizona’s Altar Valley, Tim “Nailer” Foley — a wizened desert rat with piercing blue eyes — heads up the Arizona Border Recon, a militia group bent on keeping Mexico’s drug wars south of the Rio Grande. And in Michoacán, Dr. Jose “The Doctor” Mireles rousts a popular uprising known at Autodefensas, armed citizens who move from town to town driving out members of the Knights Templar.

With little narration and superb editing, Heineman’s film jumps back and forth between the two vigilante groups, offering us tense moments of armed combat, torture and — in one harrowing scene — a late-night execution, alternating such action with up close and personal footage of the group’s members as they navigate the political landscape.

Although interesting, the exploits of “Nailer” along the U.S. border aren’t nearly as compelling as the epic story of Jose Mireles, whose rise and fall as the leader of a popular revolt seems to encompass, in microcosm, the universal tragedy of political resistance. Charismatic and well-spoken, Mireles is the classic hero (complete with Achilles heel) who confronts a series of increasingly malign obstacles — infighting, betrayal, corruption from within and without, a possible assassination attempt — in his fight for freedom from terror.

It’s difficult to think of a modern documentary as complex and well put together — not to mention as morally confounding — as Cartel Land, a documentary whose “facts” are stranger, and more compelling, than most fictions about the drug wars. Not since HBO’s excellent series The Wire has a piece of entertainment so relentlessly shown us tangled truth about crime and crime fighters.  (Bijou Metro)