Nutshell: I believe we've seen Klingon honor about 100 times now, but this brotherly tale is surprisingly poignant.
Worf's brother Kurn (Tony Todd) comes to DS9 to ask his older brother to kill him according to the Klingon Mauk-to'Vor ritual—allowing him to end his destroyed and dishonored life and enter an honored and dignified afterlife.
"Sons of Mogh," contrary to the stale superficiality that the previews suggested we were in for, is a well-written human story about purpose and duty, highlighting how the problems between the Klingons and the Federation are affecting individual lives—specifically those of the sons of Mogh.
Because of Worf's siding against Gowron in "Way of the Warrior," Kurn's once-honorable life in Klingon civilization has since been taken away. The family's land was seized by the government, the name stripped of title, and Kurn lost his seat on the High Council. He has become a man with no purpose nor allies. So Worf obliges his brother and plunges the knife into Kurn's chest. But Dax realizes what's going on and intervenes; Kurn is beamed to the infirmary in timed to be saved.
Sisko is not happy with Worf's attempted killing (I don't think I've seen the captain chew out an officer as severely as he does here). Murder, as Starfleet would likely see it, is not condoned in any form—despite cultural rituals and family beliefs. This leaves Kurn with a problem: He can no longer die with honor (suicide would not be an honorable death), and he has no place to go in life. Worf, trying to do the least he can do for his brother, helps Kurn get a job on Odo's security team. Given his warrior disciplines, Kurn proves adept at security—too bad he hates it.
Kurn, with his death wish, allows himself to get shot on the job. As a result, Odo fires him. ("A man with a death wish is a danger, not only to himself, but to the rest of his team," Odo says.) Kurn wakes up from his injury, cheerless to find himself not dead. Defeated, he yields to Worf: "You're the older brother. You tell me what to do and I'll do it. My life is in your hands."
Tony Todd, who delivered a wonderful performance in "The Visitor" earlier this season, delivers again as the brooding, dead-spirited Klingon. He has a quiet, low-key way about him that is effective in displaying how alone his character feels. Worf is able to give Kurn one more mission, which links to the episode's B-story, involving some mysterious explosions along the Bajoran space borders. When a Klingon ship is severely damaged by one of these explosions, Kira, commanding the Defiant, tows it back to DS9 for repairs. Meanwhile, Worf figures out that the explosions are tests of a minefield the Klingons have been laying out. Minefields are illegal, and would be a problem if the Klingons were to declare war on the Federation. DS9 and Bajor would be cut off by the Klingons.
Sisko wants the damaged ship secretly searched for the data of the mine locations. This is where Worf and Kurn come in. Posing as members of the damaged vessel's crew, they beam in and gather the data. But not before a botched confrontation with an officer aboard the ship that results in Kurn killing him, and Worf questioning whether his Klingon instincts have become dulled over the years.
In this respect, the episode is also a good Worf show. He begins to finally realize that because of the path he was forced to choose, he may never have the chance to return to the Empire. It's a personal tragedy considering what he went through to restore his honor way back in TNG's fourth season, only to have it destroyed again because of Gowron's hostile intentions. For that matter, "Sons of Mogh" also explores why Worf chose to oppose Gowron in the first place—not just because of his duty to the Federation, but his duty to the Empire. A war between the Federation and the Empire would likely have the Klingons on the losing side. So by protecting the peace, Worf protects everybody, but at a personal cost. This is good stuff.
Using the stolen data, Kira auto-destructs the Klingons' minefield. True, this B-story is hardly climactic, but like "Return to Grace," it's just another example of the Klingon presence starting to brew in a plausible manner—bigger things are likely to happen down the road, so for now this is perfectly adequate set-up material.
But Kurn is still a dead soul. In his own eyes, by siding with Worf and killing the Klingon officer, he has only dishonored himself further. Still, it's reassuring to see that Kurn understands why Worf has chosen the path with the Federation. But Kurn has nothing. He no longer belongs anywhere. This leads to Worf's and Dax's solution: Erasing Kurn's memory and giving him a new family and identity. This solution, unfortunately, just doesn't sit quite right in terms of the show. Granted, it does have an emotional impact concerning Worf (when the erased Kurn asks Worf if he is part of his family, Worf's response, "I have no family" really hits home), yet it seems too easy a solution for Kurn under the circumstances. It would have been more dramatic if the writers had come up with something a little less "sci-fi" and a little more dependent on a choice by Kurn. Is there really honor in abandoning one's identity? How is this different from killing oneself?
Objections to the ending aside, this show does a wonderful job of reevaluating Worf's position on DS9. It shows the kinds of sacrifices and consequences that make him an unsung hero. It also shows how the breakdown of the Klingon/Federation treaty has repercussions, without the obviousness of violence and death.