Robert Graves’ novel opens with Claudius (or Tiberius Claudius Drusus Nero Germanicus) introducing himself and describing his personal motivation for writing this autobiography. According to Claudius, the existence of the text was prophesied by the Sibyl at Cumae, who declared that Claudius would “speak clear” in nineteen hundred years by writing an accurate account of his life. With that in mind, Claudius assures the readers that his narrative is a factual account of all of the importance occurrences in his life, particularly the events leading to his ascension as emperor. Claudius’ autobiography is fated to tell the true story of his life to future generations, and, in the same way, his position as emperor is also pre-ordained.
Claudius begins the description of his life with the account of his grandmother, Livia, and her marriages, first to his grandfather and then to Augustus. An extremely ambitious and manipulative woman, Livia attempts to convince Claudius' grandfather to seize control of the Roman government and declare himself to be king. When he refuses, Livia forces him to divorce her and marries Augustus instead, realizing that Augustus will be much easier to manipulate in order to achieve her political goals.
Over the next several years, Livia’s influence helps Augustus to gain enough political power to become emperor. While Augustus is emperor in name, Livia is still the true power and force behind his position. With Augustus’ position firmly determined, Livia begins to focus on ways to ensure that Tiberius, the eldest son from her first marriage, will succeed Augustus as emperor and allow her to maintain her position of power. In order to fulfill Tiberius’ succession, Livia is forced to remove numerous political obstacles. She arranges for the deaths of Agrippa, Marcellus, Lucius, and Gaius, each of whom is favored by Augustus as a potential heir.
Livia even plots the death of her younger son, Drusus, because he threatens her ability to rule through Tiberius after Augustus’ death. Drusus, who is also Claudius’ father, had become a celebrated hero in the military campaigns in Germany and had sent a letter to Tiberius complaining of Livia’s influence over Augustus. Shortly after Livia intercepts this letter and sends her personal physician to Drusus’ camp, Drusus dies, allowing Livia to continue uninterrupted in her quest to make Tiberius the next emperor.
As a young child, Claudius is mistreated by the majority of his family because of his sickly nature, limp, and constant stammer. Antonia, Claudius’ mother, is particularly cruel to him, and Livia and Augustus simply refuse to be in his presence. Claudius’ only friends are Germanicus, his older brother, and Postumus, his cousin. Claudius also gains a loyal friend in Athenodorus, a kindly philosopher who acts as his tutor and teaches him the beauty of history. Claudius’ appreciation for history is accentuated when he meets the famous historians Pollio and Livy in the library. Claudius decides to model his own historical writing after the detailed and accurate accounts written by Pollio. Pollio also gives urges Claudius to emphasize his stammer and constantly play the fool around his family; otherwise, he will be viewed as a potential threat and will not stay alive in the dangerous political climate.
The Sibyl’s prophecy at the beginning of the text is mirrored in one particularly significant event in Claudius’ childhood. While Claudius and his siblings are playing outside, two eagles begin to fight in the air and a wounded wolf cub falls into Claudius’ arms. An auger tells Claudius’ mother that the wolf cub represents Rome, and one day, Claudius will be emperor. Although Antonia does not treat Claudius any differently, she realizes that Claudius will eventually be the savior of Rome, and Claudius notices that she sometimes looks at him with a strange expression.
When Claudius is thirteen years old, he falls in love with Medullina Camilla, and Augustus decides that the two should be married. Furious at Augustus’ independent decision, Livia arranges for Medullina Camilla to be poisoned and forces Claudius instead to marry Urgulanilla, the monstrous daughter of her friend and confidante, Urgulania.
After a few years, Germanicus becomes a celebrated hero in Germany just like his father. Livia begins to view Postumus as a potential threat to Tiberius and decides to frame him by accusing him of raping Livilla, Claudius’ elder sister. Although Postumus is innocent, Augustus believes Livia and Livilla and imprisons Postumus on a small island in the Mediterranean. With Postumus’ banishment, all remaining political obstacles to Tiberius disappear and Tiberius is certain to be Augustus’ heir. When Germanicus tells Augustus about Livia’s plot against Postumus, Augustus realizes that Postumus is innocent and secretly frees him from the island prison. When Livia discovers what Augustus has done, she realizes that he intends to restore Postumus to favor and remove Tiberius as his heir. Unable to allow Augustus to ruin her plans, Livia poisons him. Without Augustus’ protection, Postumus is forced to go into hiding and is eventually discovered and executed.
With Augustus’ death, Tiberius becomes emperor. At first, Livia is able to control Tiberius as easily as she had controlled Augustus, but Tiberius chafes under her influence and begins to listen more to Sejanus, the ambitious Commander of the Guards. Sejanus feeds into Tiberius’ insecurities and convinces him that Germanicus is actually plotting to take control of the government. When Germanicus successfully quells the Rhine mutiny, Tiberius becomes even more convinced that Germanicus is poised to overthrow him. Although Germanicus is innocent of any treachery, he is unable to convince Tiberius of his loyalty and is sent to Syria, where he dies under unusual circumstances. The Roman public is devastated by Germanicus’ death, but Tiberius is simply relieved that the threat posed by Germanicus’ popularity is gone.
Sejanus continues to promote his own interests after Germanicus’ death, and his ambitions grow to such an extent that he plots to overthrow Tiberius himself and rule Rome with Livilla at his side. In order to ensure that he and Livilla can successfully overthrow Tiberius, Sejanus convinces Tiberius that Germanicus’ widow, Agrippina, and their eldest sons pose dangerous threats to his power. This way, Sejanus is assured that Tiberius will remove Germanicus’ remaining sons as potential heirs to the throne. At Sejanus’ suggestion, Tiberius promptly kills or imprisons any friends and supporters of Germanicus’ family and then imprisons Nero and Drusus, Germanicus’ two oldest sons. Sejanus also plots to gain a closer connection to the imperial family by arranging for Claudius’ divorce from Urgulanilla and insisting on his marriage to Aelia, Sejanus’ adopted sister.
One night, Claudius is surprised to be invited to dinner with Livia and Caligula, Germanicus’ youngest son. Over the course of the dinner, Livia reveals a prophecy that outlines Caligula as Tiberius’ successor and Claudius as Caligula’s successor. Livia urges Claudius to promise to make her a goddess when he becomes emperor, and he agrees on the condition that she tells him the truth about all of the murders that she has committed over the course of her life.
In the meantime, Livia has become completely estranged from Tiberius and has very little power over his decisions. Yet, Tiberius is still afraid of Livia’s political influence and the damage that she could do against him. When Livia dies, Tiberius is finally free to make his own decisions and begins to exhibit all of the personal depravities that he had hidden in his earlier days as emperor. He decides to move to Capri and leave Rome in Sejanus’ hands. While Tiberius is in Capri, Antonia inadvertently discovers Livilla’s conspiracy with Sejanus and informs Tiberius. Sejanus is brutally executed, and Antonia, given Tiberius’ permission to arrange for her daughter’s punishment, locks Livilla in her room and starves her to death.
Tiberius’ heir then becomes Caligula, who develops into Tiberius’ close confidante and partner in the pursuit of sexual depravities. When Tiberius falls into a coma, Caligula steals his signet ring and proclaims himself emperor. After Tiberius gains consciousness a few minutes later, Caligula orders Macro, Sejanus’ replacement as Commander of the Guards, to smother Tiberius with a pillow.
The first few months of Caligula’s reign are prosperous: he doubles the wages of the soldiers, declares a general amnesty, and sends millions of gold pieces into general circulation. Soon after, however, Caligula falls ill with a brain fever and becomes convinced that he has metamorphosed into a god. Completely insane, Caligula embarks on a murderous terror against his family members, friends, and the general Roman populace. He commits incest with his three sisters, marries the wives of other men, opens a brothel in the palace, executes people for crimes as minor as selling hot water in the streets, forces Antonia to kill herself, executes his son and father-in-law, and even deploys the entire Roman military to fight a war against Neptune, the god of the ocean. Throughout Caligula’s insanity, Claudius is able to survive by using Pollio’s advice: accentuating his stammer and constantly playing the fool. Caligula even appears to be so amused by his stuttering uncle that he gives him the beautiful Messalina to marry.
On the day of the Palatine festival, Caligula is assassinated by several of his soldiers. During the chaos that follows, Claudius attempts to hide but is discovered by a group of guards who proclaim him to be the new emperor. Although Claudius tells them that he does not want to be emperor and attempts to escape, he is forced to accept the position and ultimately fulfill the Sibyl’s prophecy.