The action of the play involves the forces of Cato at Utica, awaiting the attack of Caesar immediately following his victory at Thapsus (46 BC). The noble sons of Cato, Portius and Marcus, are both in love with Lucia, the daughter of Lucius, an ally of Cato. Juba, prince of Numidia, one of Cato's warriors, loves Cato's daughter Marcia. Meanwhile, Sempronius, a senator, and Syphax, a general of the Numidians, are conspiring secretly against Cato, hoping to prevent the Numidian army from supporting him. In the final act, Cato commits suicide, leaving his followers to make their peace with the approaching army of Caesar—an easier task after Cato's death, since he was Caesar's most implacable enemy.