Back in 2002, Denzel Washington starred in Nick Cassavetes’ “John Q,” playing a man who effectively took the staff of a hospital emergency room hostage when his insurance company declined to cover the cost of a heart transplant for his son. High-strung and pompous, with lots of posturing and speechifying, the picture played an important issue for maximum emotional impact, and came off feeling phony. Rodrigo Pla’s “A Monster With a Thousand Heads” tackles a similar subject in a more restrained fashion, and though it doesn’t avoid the scent of melodrama, the intensity of its focus makes it a more successful jeremiad against a system that denies needed care to people to bolster the corporate bottom-line.

Jana Raluy plays Sonia, a Mexican housewife whose husband Guillermo has been undergoing treatment for cancer. It appears that an expensive drug is his sole hope of survival, but the insurance company has been dragging its heels approving the prescription. After Guillermo suffers a setback that leaves him wanting to end things, Sonia, after having failed to reach the insurance company doctor (Hugo Albores) overseeing the case by phone, goes to company headquarters to confront him in person, armed with a file of what she assumes will be persuasive evidence that will move him to take swift action in her favor. (She’s armed with something else as well.)

The doctor, however, proves distinctly unhelpful, preferring to leave for a squash game with his bosses rather than see her. But Sonia is in no mood to accept a brush-off. With her teen son Dario (Sebastian Aguirre Boeda) reluctantly tagging along, she trails the doctor home and forces him at gunpoint not only to admit company policy to save money by excluding expensive drugs from its formulary but to point her to the upper-echelon decision-makers who can quickly approve her claim. She finds two of them at the fitness club where the doctor had been heading and, after accidentally wounding a financial officer, takes the CEO captive. Her goal: to blackmail him into preparing the documents that will authorize the administration of the necessary drug to her husband. As their mission continues, mother and son get into increasingly deep trouble, since corporate procedures—as it turns out—demand multiple signatures. And a crisis intervenes that changes everything, leading to a sobering conclusion.

“A Monster With a Thousand Heads” isn’t terribly realistic—as Sonia’s desperate endeavor grows more and more complex, the narrative grows less and less plausible. But Pla presents it in a naturalistic style that helps one accept what’s happening despite the unlikelihood of it all (adding a few moments of bleak humor along the way to lighten the mostly downbeat tone). He also deliberately withholds detail about the family’s situation (even their apartment seems strangely empty) in order to make Sonia a sort of everywoman a viewer can more easily identify with (by contrast, the homes of company officials are quite opulent). Raluy, moreover, anchors the film with a performance that’s alternately commanding and timorous, shifting convincingly between the two. The supporting cast is fine, including Albores, whose Dario springs into action when his mother is threatened, and the behind-the-camera crew abet Pla’s approach: Odei Zabaleta’s cinematography, though widescreen, creates a claustrophobic feel, with some events shot from a distance to emphasize Sonia’s sense of dislocation, while Miguel Schverdfinger’s editing keeps matters clear even as the interconnected plot threads grow more complex.

Like “John Q,” Pal’s film plays to a natural antagonism against companies that exploit people’s misery for their own profit, and it makes no claims to objectivity. Unlike the earlier picture, however, by keeping the story of one person’s struggle against corporate indifference on an intimate scale it manages, despite its implausibility, to be both effective in terms of its message and dramatically affecting.