Castrovalva

Although Season 19 is, without a doubt, a very criticized season due to a new young Doctor played by the extremely talented Peter Davison and young companions, Castrovalva is one of those stories that is very enjoyable and not a dark story, like some of Tom Baker's episodes were. The Master returns in this story, evil as usual, and trying to destroy the Doctor, like he always tried before; although he was the reason why the Fourth Doctor regenerated.

Peter Davison portrays all the previous doctors marvelously, especially the Second Doctor. Tegan is actually very mild-mannered in this story, and is written quite well. Adric may seem like he is against the Doctor by setting those traps on the TARDIS, but it is against his will, because it is actually the Master's doing, not his. Nyssa is well written as well, but she tends to show off her knowledge quite a bit. 

When seen, Castrovalva seems like a well-ordered place, and also seems like an actual place as well. But yet again, the Master has something to do with this...he built it using Adrics mathematical skills. 

The Doctor finally regains some of his wits towards the end of Part Three and is able to fight the Master and save Adric. Shardivan gives up his life by helping the Doctor by shattering the web the Master created so that the Doctor is able to jump in and grab Adric. Castrovalva, without the web, falls apart and at the end of the story, we see the Master is trapped...or is he?

This story had good acting by all, and the storyline is very good for Peter Davison's first story as the Doctor. It takes a lot of good acting and skill to replace Tom Baker, but Peter Davison did a wonderful job and he truly deserves the credit which few people do not give him.