El Maestro is an idealistic Chicano studies instructor at a junior college in a small rural town. Despite dwindling classes, he is determined to bring to light the many injustices within their community and inspire political action. But his students don't care; they want to party on Cinco de Mayo. Aside from his star pupil, Magdalena, the rest of the class laughs at El Maestro and his outdated views on Chicanos and activism. But El Maestro remains positive and confident that his guidance can still steer them toward meaningful change.
Upon planning a Cinco de Mayo protest against a rash of racially motivated violence against Mexican immigrants involving flag burning and an unsolved murder, Dean Liberstein thwarts him. The Dean accuses El Maestro of being a 'racist radical' and a trouble maker. With his life's work deemed 'obsolete', he is fired.
Fearing for his mental health, the Dean sends him to the office of Dr. Harry Love, a psychiatrist who determines that El Maestro is unknowingly suffering from a rare disorder known as Aztec Blood Lust. Dr. Love warns that it's only a matter of time before he explodes with homicidal rage and urges him to act it out in his office to exorcise his blood lust. El Maestro refuses to believe Dr. Love's claims and bolts out of his office.
But soon after humiliating exchanges with his racist neighbor Ted, and the local Sheriff, he begins to hear voices in his head, beckoning him to kill. Armed with a knife (given to him by Dr. Love to use as an exercise tool) and a Day of the Dead mask (given to him by Magdalena) he falls into a catatonic state and begins to stalk and execute his enemies. He begins with his neighbor Ted and then Dean Liberstein.
With the body count rising, and fearing a racial revolt, a posse is formed to find the killer. The Sheriff orders the posse to stand down but they are defiant and will stop at nothing to restore order to their town. The Sheriff finds a clue that leads him to Dr. Love. After much interrogation, Dr. Love finally breaks and tells the Sheriff the horrible truth: he and Dean Liberstein were provoking El Maestro to commit violence as a social/racial experiment. But it worked too well and now he is an unstoppable killing machine. The Sheriff races to find El Maestro before it's too late.
Meanwhile, El Maestro's students are having a Cinco de Mayo party at a farmhouse when the vigilante posse arrives and tries to assault them. As tension between the two groups starts to run high, El Maestro strikes and kills the vigilantes, impaling one of them on a flag pole with the Mexican flag waving in the breeze. El Maestro tells his former students that he murdered these men to show them that heroes do still exist, and that this was his destiny. The Sheriff shows up and pleads with El Maestro to come quietly. El Maestro charges at the Sheriff with extreme force and is shot down. The students gather around El Maestro's bullet-riddled body with sadness and disbelief. Two male students aren't so sentimental; they scoff at El Maestro's actions. As they talk trash, El Maestro rises back from the dead and grabs the two students and they scream. Freeze frame. The end?
