The plot is Smiley breaks into the prime universe and conscripts O’Brian to come back with him and fix the beaten-to-shit ISS Defiant for one last battle to save the newly-democratic Terra.

I hate the mirror universe with a passion. It is by far my least favorite plot device in all of Trek.

Plot device? It has less than nothing to do with actual plot elements within any of the shows. Usually it’s just a fun “what if” kind of thing ranging from moral philosophy to just having a fun romp.

It became a major part of the entire Discovery tv show.

That example only shows how shite Discovery is, that it could taint such a timeless trope as the mirror universe. 🤌🏼