In 1933, Cuba has suffered seven years of terror perpetrated by a regime of corrupt politicians led by President Gerardo Machado. Threatened by a growing revolutionary underground, the senate passes a bill making all public gatherings a crime. One day a group of students, including Manolo Valdes, is caught distributing anti-government leaflets and chased by the political police called the Porra. Manolo escapes, but one student is shot and captured. Manolo, fearful that his identity will be revealed, goes into hiding, but first arranges with his sister China to signal him if the police do not come for him. The following day, China indicates that all is well, but as Manolo enters the university, he is killed by the police while China watches in horror. Later, China joins the underground, determined to take revenge on her brother's killer. At one of the group's meetings, she meets Tony Fenner, an American, and volunteers to participate in his plan to assassinate the Cuban leadership. Her first assignment is to withdraw money from Tony's account at the bank where she works. That same day at the bank, Porra agent Armando Ariete asks to examine all American accounts. China recognizes him as the man who killed Manolo, but maintains her composure. Later, Tony reveals his plan: The volunteers, consisting of Guillermo Mantilla, Ramón Sánchez, Toto Berenguer and Miguel, will tunnel from China's house to the cemetery. Tony will then assassinate a popular member of the government, and while all the other government officials attend his funeral, will explode a bomb underground, killing all of them. China warns Tony that because Contreras, the man he intends to kill, has a reputation for being better than the rest of the government, some members may object to his murder, but Tony will not make another choice. After the meeting, China and Tony, who have begun to fall in love, have breakfast and are seen by Ariete, who recognizes Tony's name from the bank. While work begins secretly on the tunnel, Ariete keeps close watch on China. One night, Ariete arrives at China's house, bringing food and flowers. Under the influence of too much rum, Ariete plays Russian roulette and then begs China to make love to him. Although Tony is prepared to intervene, Ariete passes out. As the digging continues, Ramon, a student, has second thoughts about killing Contreras when he remembers how, as a small boy, he used to play with his son. He becomes increasingly disturbed and wanders around the streets, begging people to prevent the murder. China and Guillermo find him, but he breaks away from them and is hit by a truck and killed. Later, at the bank, Ariete questions China about Tony, whose family was Cuban, and threatens to arrest her if she does not turn him in. Finally, the tunnel is completed, and Contreras is killed. Tony's plans fail, however, when Contreras' family decides to bury his body at a different cemetery. China offers to withdraw Tony's money from the bank so that he can leave the country, even though Tony, who is angry at his failure, does not want to leave. When China cashes Tony's check, she is fired, but before she leaves, she secretly gives the money to another employee to deliver to Tony. When she returns home, however, Tony is waiting for her, and when China tells him that Ariete is outside, he decides to die fighting and a gunfight ensues. Using dynamite that was intended for the bomb, Tony and China are able to drive the police away, but Tony is fatally wounded in the battle. Before he dies, however, he hears the city bells ringing, indicating that the revolution has begun.