When Tahna (Jeffrey Nordling), a former member of a Bajoran terrorist group, seeks asylum from Sisko after a narrow escape from Cardassians who have labeled him a criminal, he begins carrying out a new plan that involves gaining the trust of his old acquaintance, Major Kira. The most interesting aspect of "Past Prologue" is that it introduces the many shades of grey that define some of the strongest aspects of the series. The heated arguments between Sisko and Kira highlight how much of an asset that conflict between regular characters can be on DS9.
Meanwhile, the episode introduces "plain, simple Garak" with an amusing, unforgettable opening sequence between him and Doctor Bashir—and continues to develop Bashir's energetic kid-like naivete. Kira and Odo show an interesting understanding in a standout scene that reveals Kira's problem of being torn between her loyalties to the "old" Bajor and her loyalties to the ever-evolving provisional government that has made its alliance with the Federation.
Plot angles involving Tahna, Garak, the Cardassians, and even the Duras sisters tie together with surprising plausibility, leading to an episode that goes a long way toward defining characters and relationships while being quite entertaining all the same. Only the lack of development in Tahna as a character holds this one back.