the story: A rogue Trill seeks to pilfer the Dax symbiont.
what it's all about: The highly unfortunate thing about the timing of airing "The Siege" and "Invasive Procedures" back-to-back at the beginning of the second season is that they both feature the station getting evacuated, so it creates a situation where you've kind of got to decide which is the better version of the story. On the one hand, you'd think "Siege" would come out on-top because it's the conclusion of the ambitious three-episode arc that is itself a huge selling point. But the thing is, "Siege" seems thrown together and unearned. "Invasive Procedures" on the other hand seems anything but.
The key difference is that the good guys have a dilemma that directly involves them this time, rather than merely the unwitting center of a crisis that otherwise doesn't really involve them except by choice (yay generic hero situation!). And actually, "Procedures" is the soft beginning for what became one of the defining character arcs of the series, the trouble of Trills without symbionts.
The Next Generation episode "The Host" introduced the concept of the joined Trill species, but it was Deep Space Nine that really had a chance to run with it, thanks to having Jadzia and then Ezri Dax as series regulars. Jadzia would run into more problems of this kind in "Equilibrium," and then there was Ezri herself, the next host after Jadzia of the Dax symbiont, who embodied the problems of new and/or unprepared hosts. (In case it slips your mind, but the reason Sisko tends to call Jadzia "Old Man" is because he knew the host before her, who was an old man.) Ezri experiences the same problems in "Field of Fire," all the way in the last season.
So that's considerable reach for the problems "Procedures" addresses. The Trill in Deep Space Nine were more fully developed than in "The Host." "Equilibrium" is a better episode than "Procedures," but "Procedures" features a more memorable villain, mostly because he's played by John Glover, and has the future Tuvok in Voyager, Tim Russ, supporting him in one of Russ's several minor appearances before becoming a Star Trek regular. In the end, it's all about hubris, not having any idea what the problems really are in what Glover's character is trying to accomplish. Pretty standard storytelling, but it helps bring the characters together in a way that hadn't really happened previously in the series. In a way, if you want to overlook the three-parter, or consider it an extension of the first season finale ("In the Hands of the Prophets") you might think of "Procedures" as the real second season premiere.
franchise- This is pretty series-specific.
- series - Could easily function as the easy entry point of the season.
- character - Important for the future of the Dax symbiont.
- essential - Okay, pretty important!