V3 - Devil's Planet

One can easily tell right off the bat that Katarina was just not going to fit in with the show. The character has absolutely no footing in the new, futuristic world that she finds herself in, and her superstitions and primitive beliefs prevent her from joining in on any conversation. The Doctor seems to think so, too. If it was anyone else (especially a male), he (well, Hartnell's Doctor, anyway) would have been quickly dismissive of the young handmaiden, and, in the few, brief scenes that The Doctor and Katarina share together in this story, it's almost like an adult talking to a small child.

I'm not sure what producer John Wiles and script editor Donald Tosh were thinking when they thought up the idea of a character from ancient times becoming part of the TARDIS crew, but at least they realized their mistake and ended the experiment quickly. The detour to the prison planet Desperus (where things are desperate, in another subtle naming convention from Terry Nation) is here pretty much exclusively to set up Katarina's impending death. (Some dialogue that was cut from the final product was meant to emphasize this even more).

And yet, despite the deviation from the plot, it still doesn't feel as tacked on as much as, well, any sequence from The Chase. This is mostly because what Mavic Chen brings to the table, but I've got a good few episodes yet left to talk about him, so why spoil that now?