The week of his 18th birthday, Bennie, who's a waiter on a cruise ship, has a layover in Buenos Aires. He seeks out his older brother, Tetro, whom he hasn't seen in years. Tetro, who lives with Miranda, is a burned-out case; he's hot and cold toward his brother, introducing him as a "friend," refusing to talk about their family, telling Bennie not to tell Miranda who their father is. Thoughts of their father cast a shadow over both brothers. Who is he, and what past has Tetro left behind? Bennie finds pages of Tetro's unfinished novel, and he pushes both to know his own history and to become a part of his brother's life again. What can come of Bennie's pushing?

In this suspense thriller, Stephen Boyd plays Miguel, who is clearly not in his right mind. He remembers killing his mother-in-law but cannot determine what happened to his wife Pilar (Marisa Mell). As far as he knows, she may have just run away. As the film opens, it is the servant's day off. Marta (also Marisa Mell), a good-looking young woman who is the spitting image of Miguel's wife, runs the gauntlet of his snarling dogs. He rescues her and puts her to bed in a very fatherly fashion. Later, she tries to seduce him, but he has some sexual dysfunction which causes her efforts to fail.