Although Michael Eddington's swan song would come next season, this is the episode where he goes from being a conscientious, competent security officer into a full-fledged villainous rebel. The above quote, courtesy of Eddington, shows just how far the show had come from its Star Trek forbearers--that it was not a Romulan, Cardassian, Klingon or Ferengi complaining about the Federation's cultural imperialism, but a human and, wait for it, a Starfleet Officer!
That's not what the episode is about, though. It focuses mostly on the Sisko/Kasidy relationship. There is a suspected Maquis smuggler on board, and Sisko is told that it might be Kasidy. They proceed slowly, as the seeds of doubt begin to grow in Sisko's mind. There is one scene which particularly struck me--it's the one where Sisko asks Kasidy to drop everything and go to Risa with him. Sisko is acting out of love--he doesn't want Kasidy to get hurt and wants to give her a way out. Kasidy is acting out of duty, which trumps her love for Sisko. Sisko knows this, and knows that she could never accept. So why ask? It just tells us something about Sisko.
However, the Sisko/Kasidy plot isn't what people remember about this episode. It's Eddington, the scheming, revolutionary Canadian security officer-turned-Maquis. His character would return for two excellent episodes in Season 5: "For the Uniform" and "Blaze of Glory".