If you don't know much about the Mirror Universe and would like to know, one place to start is Star Trek dot com, which is the Paramount page for the shows. It isn't the best site in the world, but it does provide a bit of info.

For example, the second (perhaps third) adventure in the Mirror Universe (the first being in the original show's Mirrror Mirror) is DS9's Through the Looking Glass.

Read about it, and the various follow ups. Don't watch it. It is stupid. (there is one cool bit where the realworld Sisko makes his own technology available [they should, of course, have it already] and they build a Defiant. It kicks everyone's ass)


And for those about to comment to the effect that I am a nerd: (I quote August J Pollak) Fuck the fuck off.