An old Cardassian anti-takeover program runs amok on DS9 and locks down the entire station. As the crew attempts to regain control, they make matters worse, leading the program to attack civilians and eventually arm the auto-destruct sequence.
Although a general Trek rule of thumb states that any plot involving a self-destruct sequence is asking for trouble, the real problem with this episode lies within its uneven story structure and cliched jeopardy premise of a countdown to disaster. "Civil Defense" is a watchable but weak entry into the season.
During a routine analysis of the file system, O'Brien inadvertently sets off a programmed defense routine put together by Gul Dukat during the Occupation. Further complicating matters is the fact the program has so many fail-safe devices. Every time the crew attempts to regain control, a new subroutine takes over, with worse intent than the last. This eventually leads to a two-hour countdown to self-destruct.
This is yet another Trek example of "computer goes berserk." The premise of an old program surfacing from nowhere is hard to swallow because any computer-literate person knows that you completely wipe all old software from a used storage device before putting your own software on. Are we supposed to believe that such a hazardous program went totally undetected by Starfleet when they took control of the station?
Granting the story this detail only improves things slightly. The jeopardy premise is really worn out (although this is the first time an auto-destruct has been armed on DS9—I suppose it had to happen sometime). And structuring the story into three separate threads doesn't work. Kira, Bashir, Garak and Dax try to regain control of Ops while Sisko, O'Brien and Jake try to escape a room they're trapped in by using MacGyver-esque resourcefulness.
The A- and B-stories alone may have worked okay with a little better pacing, but the writers also introduce a C-story with Odo and Quark trapped together in Odo's security office. Their role in the narrative has no dramatic purpose nor does it contribute to the advancement of the plot. The duo is used only as gratuitous comic relief and, unfortunately, scene after scene between them falls flat. Put simply, the three plots pull each other down because each interrupts the flow of the other (and, really, the C-story should have been scrapped altogether).
Gul Dukat boards the station to gloat and strike an unreasonable deal in exchange for deactivating the self-destruct device. Mentionable is how exaggerated Alaimo's performance is. It's not up to par as was his commendable outing in "The Maquis." This time around, Alaimo spends so much time constructing his sentences and speaking so distinctly that it's distracting and almost hokey.
Fortunately, Dukat gets some worthy moments. A great touch is when he flips Sisko's baseball off the prefect's desk with his forefinger. And in the episode's best moment, he becomes a victim of wry irony when yet another fail-safe device locks him on the ticking time bomb with everyone else.
The most interesting part of "Civil Defense" is the bad blood between Garak and Dukat, who exchange insults and blather of the past through most of their scenes together. But just as with all Garak backstory, there is no backstory. It's just a lot of unexplained, half-hashed dialogue that may or may not be developed in the future.
The conclusion boasts one of those down-to-the-wire endings in which Sisko rewires the reactor core so it won't destroy the station. But there's nothing fresh about an ending where the hero saves the day with only five seconds left. It's been done too many times. Nevertheless, even this tired scene could've received an energy boost from an exciting score. Instead, we get the usual form of linear monotony.
This episode also lacks an effective coda. The biggest mistake is that the writers don't work Dukat into the ending, making his role in the episode feel disturbingly unfinished. Instead, we get a wrap-up of the Odo/Quark plotline—bordering on pointlessness.