This is a small paperback that is essential to fans of the original Star Trek TV show. It provides good summaries of all the episodes so if you've forgotten the basic plots you can get reminded.
I'm not sure if this is true, but this may have been the first published guide to all of the episodes of the original series. In any case, this book was my only reference guide to the original Trek, back in the days when I cared. I remember finding it at a local bookseller's back in the '8os, a store that is long since defunct, and being rather excited at finally finding a good episode guide. Along with the complete episode guide there are several essays about many aspects of the Trek universe. A nice, compact reference.
Some of the articles are interesting, other extremely boring, and some are just wrong as most of the arguments can be disconfirmed with certain episodes. But metatheory is always a good thing. Well almost always.