The Imperial Army on the Rhine has been wiped out and Tiberius sent to avenge the defeat, followed later by Germanicus. Livia has discredited Postumus, who has been banished. Augustus has been feeling unwell, but is avoiding suspicions of poisoning by eating figs from his own garden.

Germanicus has been murdered in Antioch and his wife Agrippina is convinced Tiberius ordered the killing. Livia has discovered that Caligula helped to poison his father. While Tiberius's perversions have become notorious, his right-hand man Sejanus, commander of the Praetorian Guard, gathers more power for himself, including a marriage alliance with Claudius.

With Tiberius retired to Capri, Sejanus plans to tighten his grip on Rome and divorces his wife so he can marry Livilla. But he also has powerful enemies and his attempts to consolidate power set in motion a bloody chain of events.

Caligula's erratic behaviour continues, as he makes his horse a senator and turns the palace into a brothel. Many in the Praetorian Guard grow to realise that their ruler is insane and, fearing the collapse of Rome itself, believe that something needs to be done.

Claudius has ruled wisely for a year with the support of Messalina, whom he deeply loves. Convinced of her devotion, he is totally unaware that she is deceiving him.

Almost at the end of his family history, Claudius' thoughts turn to the future of Rome.