“Tribunal” is episode twenty-five of season two of Star Trek: Deep Space Nine.
Chief O’Brien and his wife Keiko are taking their first vacation in years, without their daughter, although O’Brien has to be practically pushed out of the station. As O’Brien makes his way to the runabout, he passes a person he used to serve with and exchanges greetings. After O’Brien leaves, the man behaves rather oddly.
During their journey, O’Brien’s runabout is stopped by Cardassians, who arrest him and take him back to Cardassia Prime for trial. The Cardassians refuse to tell him what he is even accused of until the trial – and the outcome of his trial is already known, as his execution is already scheduled.
It turns out that O’Brien is accused of, and has already been sentenced for actually doing, supplying the Maquis with weapons – and there are photon torpedoes missing from DS9. Odo and Keiko go to Cardassia Prime – Keiko as O’Brien’s spouse and Odo because he’s an officer of the Cardassian courts.
They have to not only prove that O’Brien is innocent, but get the Cardassians to actually release him, because the Cardassian legal system never finds anyone innocent – it’s solely there to punish those determined to be guilty beforehand.