The episode opens with the most easily summarized teaser ever, as the Cardassian freighter Bok’Nor explodes while departing Deep Space Nine.

The initial investigation into the Bok’Nor’s destruction is inconclusive, though some of the evidence suggests sabotage – and more troublingly, there is residue from a compound only used in Federation technology. Starfleet sends Cal Hudson – an old friend to both Dax and Sisko, as well as an attache to the newly created Demilitarized Zone along the Cardassian border – to the station to assist the investigation and gauge the likelihood of a retaliatory attack. Privately, Hudson confides in Sisko his frustration with his assignment to the DMZ. He has been tasked with assisting the citizens of Federation colonists whose worlds were ceded to the Cardassians adjust to their new circumstances. Hudson, however, believes that the Federation is abandoning these people in the interest of a bad treaty. He adds that while he doesn’t believe the Cardassians will retaliate for the Bok’Nor’s destruction per se, some sort of response is inevitable. Meanwhile, a Vulcan woman named Sakonna meets covertly with the Bok’Nor saboteur (try saying that three times fast) on the Promenade. She informs him that arrangements have been made for his escape and then heads for the bar, where she invites Quark to dinner to discuss a business proposition. As she does this, the saboteur is abducted from the habitat ring.

Sisko returns to his quarters for the evening and finds Gul Dukat waiting for him. Dukat tells Sisko that he has come to the station without the Central Command’s knowledge in order to help him uncover the truth about the Bok’Nor. Specifically, Dukat believes that renegade Starfleet officers are to blame and asks Sisko to accompany him to the Volan Colonies in the DMZ so that they might find proof. Sisko agrees and the two depart in a runabout. While en route, they pick up a distress call. A Federation merchant vessel has been attacked by a pair of Cardassian attack ships. Dukat is incensed, insisting that they have not been authorized to violate the treaty. His attempts to hail the attack ships are ignored, and Sisko prepares to intervene. Before the runabout can do much of anything, though, a Federation ship arrives and quickly dispatches the Cardassians. Though the two are left with plenty of questions, it is more clear than ever that despite the ignorance of both their governments, the Demilitarized Zone is anything but.

Quark meets with Sakonna and is surprised to find that she is interested in buying weapons, and lots of them. On Volan III, meanwhile, Hudson and his Cardassian counterpart Gul Evek are engaged in a heated debate with the colony council. when Sisko and Dukat arrive. The two describe the skirmish they witnessed, and the polarization is obvious, as both sides leap to the defense of their respective colonists. Evek then dramatically produces a recorded confession from William Patrick Samuels, the man who sabotaged the Bok’Nor. He adds somewhat unconvincingly that Samuels killed himself after confessing, prompting one of the Federation colonists to try to attack Evek.

Later, Hudson again voices his suspicions of the Cardassians and suggests to Sisko that the Bok’Nor was carrying weapons intended for Cardassian colonists. Sisko notes that if Hudson is right about the Cardassians arming their colonists, the Federation has diplomatic options available to stop them, though Hudson scoffs at the prospect. As they make their way back to Deep Space Nine, Dukat admits to Sisko that while he knew about Samuels’ confession ahead of time, he was caught off guard by the “suicide,” having cautioned Evek against “allowing” his prisoner to die. He also swears on the lives of his children that the Bok’Nor wasn’t transporting weapons.Upon returning to the station, O’Brien confirms to Sisko that the bomb that destroyed the Bok’Nor was of Federation origin. As Sisko prepares to inform Starfleet, Kira’s frustration with the Federation’s seeming unwillingness to defend the colonists in the Demilitarized Zone boils over. She knows from personal experience, after all, what those colonists are going to have to live through. More than that, though, she’s confident that the Cardassians can’t be trusted to live up to their part of the bargain in the new treaty. After getting Quark to reschedule the weapons shipment for that night, Sakonna joins a group of colonists in kidnapping Dukat.

Later, the crew determines that the kidnappers got off the station by forging their ships registry. As Sisko prepares to return to the DMZ, this time accompanied by Kira, O’Brien, and Bashir, they pick up a transmission in which a group calling itself “the Maquis” claims responsibility for both the kidnapping of Dukat and the bombing of the Bok’Nor. The officers give chase in a runabout, leading them to a class-M asteroid near the Badlands, an area of space rife with plasma storms and gravitational disturbances. Upon beaming down to the surface, they are quickly surrounded by a group of armed Maquis fighters – lead by Hudson.