The Enterprise is informed by a Cardassian warship captain, Gul Macet (Marc Alaimo doing the Gul Dukat performance without the Gul Dukat story baggage), that rogue Starfleet Captain Ben Maxwell (Bob Gunton) of the USS Phoenix is attacking unarmed civilian targets along their border. This is in defiance of a recently brokered treaty that ended a bloody war between the Federation and the Cardassians. (The Federation is apparently so vast that it was recently at war with another power that we'd never even heard of until now.) Picard must find and stop the Phoenix before the violence escalates and threatens to destroy the peace treaty.
"The Wounded" is a good story about the effects of war that I wish would've been even better — either more tense, or less obvious. Best about it, and most crucially, is that it's the breakout story for O'Brien, who is treated like a full-fledged regular character rather than just "the transporter chief." It reveals him as having a history and opinions, and it even ventures briefly into his life as a newlywed. (I enjoyed the Miles/Keiko discussion over breakfast, which was about breakfast.) He served under Maxwell during the war and knows him best among anyone on board the Enterprise. O'Brien's coldness toward the Cardassians is explained in a solid scene where he talks to one of them about the day during the war when he was first forced to kill an enemy: "I don't hate you, Cardassian. I hate what I became because of you."
"The Wounded" is also a crucial establishing point for the Cardassians and thus an interesting step (in retrospect) in the direction of DS9. Rather than making the Cardassians simple villains, the story shows how Macet is genuinely interested in keeping the peace. Macet is about as even-tempered as aliens-of-the-week tend to be on Trek.
The same cannot be said for Maxwell, who suspects the Cardassians of secret arms smuggling along these supposedly innocent shipping lanes. On this hunch Maxwell has attacked two ships and killed 450 Cardassians. After being tracked down, debriefed, and ordered to stand down, Picard still lets him return to his bridge, which strikes me as unlikely bordering on reckless — especially since Picard knows Maxwell's wife and children were killed by the Cardassians during the war. This leads to a standoff where Maxwell detains a Cardassian cargo vessel and pleads Picard to board it and find the weapons. When Picard refuses, Maxwell threatens to destroy it. O'Brien beams over to the Phoenix to talk Maxwell off his cliff, in what's a pretty good scene.
Overall, this is a good depiction of an embittered soldier who simply cannot give up the war, even after peace has been declared. But I think "The Wounded" might've been even better if Maxwell were not so clearly unhinged. I also think the twist at the end implying the Cardassians are actually guilty of Maxwell's charges is somewhat counterproductive to the point of the episode.