"SOMEWAY, SOMEHOW, everybody has gotten corrupted," says a Mexican man in Cartel Land, a black bandana hiding his face. "It's just a never-ending story." And it's a never-ending story that's inextricably linked to another—the "war on drugs," which continues to be waged, even as, in places like Oregon, we take baby steps toward something a little more sane.

Matthew Heineman's strikingly shot documentary hops back and forth over the border: In Mexico, we spend time with the Autodefensas, a group of gun-toting vigilantes intent on protecting Mexican towns from powerful drug cartels. And in Arizona, we spend time with the Arizona Border Recon, a group of gun-toting vigilantes intent on... well, they're definitely intent on keeping Mexicans out of Arizona. Also maybe they want to fight cartels, somehow? Also sometimes they mumble racist stuff. Needless to say, the Arizona Border Recon—dressed up in military surplus, play-acting at being soldiers—are moderately terrifying. But so, it turns out, are the t-shirt-clad Autodefensas, who might not be as free of corruption as they claim. Cartel Land lingers on the parallels between these groups, and though the film can be uneven, it's anchored by two magnetic personalities: In Arizona, there's the steely-eyed, leather-skinned, former meth-head Tim "Nailer" Foley; in Mexico, there's the charismatic, magnificently mustached Dr. Jose Mireles, vigilante by night and doctor by day.

While Heineman lets us know how high the stakes are—at least in Mexico, where we see severed heads and puddles of blood—Cartel Land's most interesting moments come not from the intense action he captures but the complexities of the situation. In Mexico, we see what appears to be an entire town turn against the Autodefensas. "You are usurping the law," one resident cries, "and it's not your place to do it! If we don't believe in institutions of the state, we are finished as citizens!"

Neither Mireles nor Nailer have time for—or, seemingly, any interest in—such debates. Both are furious at their governments' perceived inaction, both are armed to the goddamn teeth, and both see themselves as nothing less than heroic martyrs. "The odds are stacked against us, and we're sick and frickin' tired," Nailer says. "We're going to keep pushing against the cartels. I believe what I am doing is good, and I believe what I'm standing up against is evil."