Caesar has agreed to spare his life if he surrenders Utica immediately. Cato retorts that he will be merciful enough to spare Caesar's life if he surrenders now and stands trial in the senate. He then sends the envoy away. Juba arrives and praises Cato's strong leadership, prompting Cato to express gratitude for Juba's loyalty. Cato promises to give Juba whatever he wants as repayment for his service when the war ends. Juba shyly asks to wed Marcia, but Cato is affronted by the notion of Marcia marrying a Numidian and storms off. Syphax arrives, and Juba laments that Cato will not consent for him to marry Marcia. Syphax once again urges Juba to marshal the Numidian armies and overthrow Cato, and suggests that once Cato is dead he can take Marcia as his prize. However, Juba vows that he will remain an honorable man and win Cato's favor fairly to marry Marcia. Syphax worries that he will never be able to persuade Juba to turn against Cato. Marcus, still unaware of Portius and Lucia's affair, comes to Portius and begs him to convince Lucia to wed him. Portius does not reveal his relationship with Lucia to Marcus. However, after the brothers' conversation Portius goes to Lucia and informs her how much grief Marcus is in because of his unrequited love for her. Saddened by this news, Lucia decides to end their affair before it brings any more misfortune to Cato's already-suffering family. Portius returns to Marcus and tells him that Lucia feels compassion for him but has sworn off romantic love and cannot be with him, and a heartbroken Marcus pledges that if Lucia will not be his, he will die fighting his father's enemies, rather than live without her. In the Senate, Sempronius grows tired of waiting for Syphax to turn Juba's allegiances, and raises his own mutinous legion to overthrow Cato. He sends them to arrest Cato, but when Cato is confronted, he makes an impassioned speech that moves them to release him. Sempronius realizes Cato cannot be deposed by troops so loyal to him and resolves to abandon his plot, abscond with Marcia, and leave Utica to join Caesar's legions. He dresses as Juba to gain entry to Marcia's apartments. However, Juba himself finds him first and, realizing his treachery, kills him. Marcia finds Sempronius' body and, believing it to be Juba's by his dress, confesses