Although I don’t agree that Deep Space 9 was the best Star Trek series out of the 5, I do understand that it’s episodes like this one that feeds that particular opinion. And what a powerful & well acted episode it is!
Duet is the 19th episode of the 1st season of DS9 and features a Cardassian man who comes to the station for the purpose of getting arrested by Major Kira Nerys. The reason is that the man who is actually Marritza, a clerk in a former labour camp where Cardassians tortured Bajoran prisoners of war, has been torn with guilt for not doing anything about the atrocities committed in the camp. So after he learns of the death of the camp warden, the notorious butcher Gul Darhe’el, he has his face surgically altered to resemble the dead tyrant. He also seeks out Kira’s station, knowing that there he would be apprehended and convicted. Imagine a Nazi German being ashamed for not doing anything to stop the killing of Jews in a camp and you get the picture.
Ashamed of being a coward in his own eyes, Marritza wants to be killed by Bajoran judicial systems to atone for the fact that he did nothing to prevent the killing of innocent prisoners. A powerful rant & rave proceeds between Marritza (acted by veteran actor Harris Yulin) and Kira (played ofcourse by Nana Visitor) while the former is at the heights of pretending to be Darhe’el. He taunts and verbally torments Kira for being a Bajoran and shows contempt and superiority complexes. However when Kira finally understands that he is infact Marritza, an even more moving & powerful dialogue ensues.
Marritza at first still claims to be Darhe’el but breaks down as he states about his own shame at being crowdly and not doing anything to help the prisoners. He wanted to be caught & punished and hence setup this elaborate ruse. Kira has him released but Marritza is killed by a Bajoran as they try to get the Cardassian off the station.