Professor Moriarty wrote:
Seems pretty straightforward to me. (Spoiler warning!)
The Exeter tangles with some Tressaurians, a reptilian race the Captain encountered many years ago. These nasty lizardfolk have stolen a Tholian device that is capable of shifting objects into another dimension. When Exeter follows the Tholians to their home base, they discover a similar device millions of times more powerful that is using a star for a fuel source. This device is capable of shifting whole sectors of space into another dimension.
And that's where we left off two years ago.
Great summary! I was going to attempt to answer that question, but when I read your post, Professor Moriarty, I realized there was no point. You explained it very well and in far fewer sentences than I would have used!