Jo gets put into a prison cell, escapes, gets put back. The Doctor and friends arrive, get captured, get put into prison cell, escape. Yay! No more prison cells in this story! Yippee! At last! The Daleks put in a "surprise" appearance as allies of the Master. You know what would have been really cool? A story where the Master and the Daleks worked together for the entire story. Would have been interesting to see how the Master would have put up with the "stupid tin boxes". There's a very confusing climax, where the Master just sort of disappears through editing and the Ogrons run away scared. The Doctor is wounded and escapes into the TARDIS, sending a telegraphic SOS to the Time Lords, and we finish the story on this cliffhanger.
Reluctantly I have to give this story a thumbs down. I used to have a much better opinion of this story, but perhaps that was from the Target novelization. Malcolm Hulke has done much better than this. Some interesting ideas, and a great new alien race in the Draconians, but way too much padding and way, way, way too many prison cells.
A brief word here about Roger Delgado. He is one of the main reasons I hold the Pertwee era in such high regard. His suave, charming, evil Master is one of the highlights of the entire series. And from all accounts, he was one of the nicest guys off the set as well. It's a shame that his final appearance was in this story, and he didn't get a proper swansong to close out his time as the Master. A tragic car accident cut his life short way too early not long after this story was shot. In some ways, it was the beginning of the end for the Pertwee era.