I wonder why the writers of this episode chose to include a second sub-plot (Garak and Ziyal) -- the main plot (Eddington-Sisko-Kasidy) is so good that it could have probably been stretched into a full episode. On the plus side, this means that the main story is perfectly executed; there are no slow spots.
Early in the episode, Sisko is informed by Odo and Eddington that his girlfriend is suspected of smuggling cargo to terrorists (the Maquis). Sisko is extremely skeptical, but grudgingly allows security to investigate. At several points through this episode, you can see Sisko bend (but not break) his duties as a Starfleet Officer on Kasidy's behalf. He waives a thorough search of her ship (but orders the Defiant to follow her ship and establish her connection to the Maquis); he tries to persuade her to forgo a second mission. I have to admit that I feel weird seeing Penny Johnson in this role, as I'm used to her playing Sherry Palmer. But she does a good job.
The plot takes a fascinating twist when it turns out that Kasidy is small fry; Eddington uses her as a decoy while he executes a major Maquis operation on the station and defects. Whoever wrote Eddington's speech to Sisko deserves serious props; it's exceptionally well done. Ken Marshall does a great job as Eddington.
The plot with Ziyal and Garak is OK. The writers took the opportunity to include a scene with Quark in Garak's shop -- probably the best part of the story.