Silius and Sabinus, respectable Roman citizens of the old stamp, meet and discuss the corruption of Tiberius’s court. Both admire Agrippina, the widow of Germanicus. Although conscious of the prevalence of spies controlled by the emperor’s loathsome favorite Sejanus, they show no personal fear. Arruntius and the historian Cordus, men of their kind, join them. Two of Sejanus’s spies watch and plan to entrap these men devoted to freedom. Sejanus enters with a group of hangers-on and suitors. Arruntius and his friends observe the favorite with scorn. One of Sejanus’s followers presents a suit from Eudemus, the physician of Livia, wife of the emperor’s son Drusus. Sejanus sends for Eudemus privately and lays plans with him for the seduction of Livia.

When Tiberius, followed by Drusus, makes a public appearance, Sejanus bathes him in fulsome flattery, to the disgust of Arruntius and his friends. The emperor answers with a devious, hypocritical speech. After his departure, Drusus and Sejanus clash, and Drusus strikes him. Sejanus remains alone, promising himself to add revenge to his ambitious motives for the destruction of Drusus. Having found Livia a willing victim of corruption, Sejanus plots with her and Eudemus to poison Drusus. Sejanus works on the fears of Tiberius to persuade him to destroy Agrippina and the sons of Germanicus, who after Drusus are heirs to the empire; he also warns the emperor of the danger of Silius, Sabinus, and others. Tiberius consents to call the senate and to allow Sejanus to handle the destruction of Silius, his wife Sosia, and Cordus, leaving Sabinus and Arruntius for the future.

Arruntius and his friends, hearing that Drusus is dying, recalls the public blow given to Sejanus. Later, the senate convenes, with Drusus’s death on all lips. Tiberius enters, to the amazement of the senators, who assumed grief would keep him from a political function. Tiberius delivers one of his hypocritical orations, punctuated by low-voiced comments from the undeceived Arruntius and his friends. Suddenly, without preliminary warning, Sejanus’s puppets accuse Silius of treason. Recognizing the tyrant’s trap and his own hopeless situation, Silius recalls his important services to Rome in peace and in war,...