The final act of the series, covering Claudius' reign, closes out with Messalina and Nero as major opponents to Claudius. They are both pretty low-grade (even clichéd) villains Messalina is an immature and foolish Smug Snake, and Nero is a bumbling caricature who is entirely directed by his mother. But given the complexity and intelligence of previous antagonists such as Livia or Sejanus, the disappointing nature of Claudius' final enemies is just more evidence of how Roman society is degrading on every level: it can't even produce good schemers anymore.
It is during Caligula's reign that Claudius gets closest to revealing his act as a silly stuttering half-wit. There are two reasons for that: Caligula is crazy so acting the fool doesn't protect Claudius as much, so he is under constant pressure to keep his wits sharp. The second reason is that Caligula was present every time Claudius did the little plotting he had, such as smuggling the letters to the emperor and causing the fall of Sejanus so Caligula knows Claudius is not as silly as he acts.
