In this dark comedy, Finn Earl (Anton Yelchin), a teenager from New York City, is planning to have the summer of a lifetime studying the Iskanani tribe in the Amazon with his anthropologist father. However, due to an unfortunate turn of events, he ends up staying in America with his mother Liz (Diane Lane), a masseuse-for-hire. The two end up living on the estate of Liz's client Ogden C. Osborne (Donald Sutherland), the seventh-wealthiest man in America. Making the best of the situation, Earl decides to conduct an anthropological study of Osborne's family.

Director Griffin Dunne carries a tribal motif throughout the film. He draws parallels between the Osborne clan and the Iskanani by interspersing documentary footage of the Amazonian tribe. The Osborne children also embrace Earl's interest in the Iskanani to the point that they openly imitate the tribesmen by wearing headdresses.

Despite the Osbornes' acceptance of Earl, he can't ignore the disparity in class differences. The film examines the social elite's separation from reality and their disdain toward those outside their inner circle. The premise isn't completely new, but Dunne does present it in a refreshing way. Rather than depict the social elite as one-dimensional degenerates, he creates complex characters - contrasting, for example, Osborne's freeloading grandson with his level-headed granddaughter.

After a shocking act of violence towards the film's end, Fierce People shifts its focus away from comedy towards a dark tale of human depravity. In spite of the turn of events, the film isn't overwhelmingly depressing. The ending doesn't offer total resolution, but it does leave room for a sense of optimism.