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 is happily married, while the mad Caligula has been assassinated. To his astonishment, Claudius has been proclaimed emperor by the Praetorian Guard.