It was the last TV story to feature Fivey and is absolutely the GOATest most epic and perfect story created for any medium ever and you can't argue otherwise or Merryfat will erase you from existence.
Additionally, /who/ rated The Caves of Andro-Rani their favourite story ever in /who/ Ranks Who 2015, so you have to like it.
Didn't I tell you how based this episode is? Watch it you fucking pleb, or I swear to me mum I'll clob ya in the gabber.
Basically Fivey runs around a bunch of corridors as in every episode before this one with him in it. This time though he's not doing it to save the world. He just wants to save Peri. Seriously, everyone fucking dies in this episode (even the silly armadillo monster and the bad guy who thinks he's on House Of Cards) except her, making her the first most important companion.
This of course begs the question of why the TARDIS, if the non-canon episode The Doctor's Wife is to be believed, brought them to Androzani Minor. Fivey does jack all except get himself killed and everyone on Androzani Minor was going to die either way. The only plausible explanation is that the TARDIS decided it was time for Five to regenerate and choke the life out of Peri, likely due to the TARDIS having sadistic fetishes for Peri.
The antidote to the spectrox poisoning was “milk from the queen bat,” so that means that the Doctor totally squeezed a bat tit. This makes him the first being depicted on the programme getting to at least second base with another species, until Capt. Jack came (ha ha) along.
Also we finally get an explanation as to why Fivey put a stick of celery on his lapel. That's cool I guess.