While leaving for a vacation with Keiko, O'Brien encounters Boone, a former crewmate from the Rutledge. The two exchange pleasantries and O'Brien hurries off, eager to start his trip. In his haste, O'Brien fails to notice that Boone has recorded his voice. Later, as he and Keiko head toward their destination in a Runabout, they are stopped by a Cardassian vessel. To Keiko's horror, Gul Evek beams aboard and arrests O'Brien, taking him back to Cardassia Prime without telling him what he has supposedly done.

O'Brien is "interrogated" by his captors until he meets Makbar, who will represent the state in the case against him. However, she refuses to tell O'Brien what charges he faces. Later, on the space station, Sisko is contacted by Makbar, who tells him that, as with all Cardassian trials, O'Brien's serves only a ceremonial function — he has already been proven guilty and will be executed. Odo, who served the Cardassians during the occupation, volunteers to serve as O'Brien's Nestor, or advisor, then Odo and Keiko set off for Cardassia.

O'Brien meets Kovat, the lawyer assigned to him by Cardassia, but he is only interested in obtaining a confession, and O'Brien still has no idea what crime he has allegedly committed. Meanwhile, Sisko and his officers discover that several warheads have been smuggled off the station — possibly to a group of Federation colonists-turned-terrorists known as the Maquis. Kira shows them that O'Brien's voice is on the security log requesting access to the weapons locker. Later, Odo arrives on Cardassia to advise O'Brien, and immediately questions him about the warheads, but O'Brien denies any knowledge of the weapons.

Back on the space station, Dax and Bashir determine that the security log recording of O'Brien's voice has probably been fabricated. When Kira arrives and tells them that O'Brien was seen talking to Boone just before the weapons were stolen, Sisko orders him brought in for questioning. Boone admits to nothing, even though he is promised protection from the Cardassians. They seem to be at a dead end, until a Maquis member secretly approaches Bashir and tells him that Boone is not one of them. At O'Brien's trial, both Makbar and Kovat continue to convince him into confessing, but the defendant remains firm. Odo attempts to introduce the evidence that will clear him, but the court refuses. Meanwhile, at the station, Sisko orders Boone to submit to a medical examination. Soon afterward, just as the Cardassian court prepares to move forward on the guilty verdict, Sisko escorts Boone into the courtroom, and Makbar suddenly announces that she will release O'Brien into Sisko's custody. As they head home, Sisko explains that Bashir discovered that Boone was really a Cardassian surgically altered to look like him. When Makbar saw him, she knew Sisko had the evidence needed to publicly embarrass Cardassia, so she let O'Brien go. O'Brien and Keiko express their relief, and Sisko sends them off on their well-deserved vacation.