Accompanied by her teen-age son (Sebastian Aguirre Boeda), Raluy's Sonia heads to the home of the doctor who denied her husband a pain-relieving drug that wasn't covered by her insurance company's formulary. Knowing that she'll likely meet with resistance, she has armed herself with a pistol.
Director Rodrigo Pla relies on our distrust of insurance companies and bureaucracy to create sympathy for Sonia, a woman who's acting out of desperation and perhaps denial about her husband's inevitable fate. < Sonia's first target is Dr. Villalba (Hugo Albores), the physician charged with coordinating her husband's care. He manages to avoid her until she's at the front door of his home.
The story then follows Sonia and the captive Villalba as they seek out various executives of the insurance company to obtain the necessary signatures for Sonia to be granted an exception that will allow her to buy the drug.
The outcome of Sonia's criminal foray is partially revealed because as the movie unfolds, we hear snippets from the court proceeding that follows Sonia's impromptu protest.
Although presented in an entirely realistic manner, A Monster With a Thousand Heads can be viewed as a fantasy of the downtrodden and frustrated, those who -- in seeking help -- are faced with stony indifference of people who act as if they are too important to be bothered with the pain and suffering of those they supposedly serve.