To make the officer exchange program an actual exchange, the Klingon first officer Kurn will take Riker's job today. But he's playing it the human way. So Riker gets to live. Here comes Kurn now...
CANDYMAN! AHHHH! Who said his name in the mirror? Not me! Cheese it! Feets don't fail me now!
Commander Kurn may not be a killer revenant, but he's pushing hard on his underlings. Except Worf. With Worf he's all smiles, honeyed words, "please" and "excellent".
He all but pats Mr. Worf on the head and seems disappointed when Worf reigns in his impulse to pop the new boss' head like a grape.
The new first officer is even polite at dinner. "I shall try some of your burned, replicated bird meat." Kurn also is "honoured" by Picard's real caviar: he wipes it off his hand onto the turkey.
Worf approaches Kurn to figure out how he has offended him.
"I am not human. If you had given offence you would not need to ask."
Turns out Kurn is Worf's baby brother. Daddy Mogh, mom, and toddler Worf were not intending to stay on Khitomer for long, so they left Kurn with family friend Lorgh. Worf's adopted father was told by the Klingon High Command that Worf had no living relatives, because they assumed Kurn was dead, too. Raised by Lorgh, Kurn only learned the truth of his origins at his Age of Ascension.
Now he needs Worf to answer a challenge laid on their family: was Mogh a traitor who sold out Khitomer to the Romulans? It's been 20 years, and Duras (the son of Mogh's rival Ja'rod) has made the challenge. If Worf fails, he will be executed, and the House of Mogh will be disgraced for seven generations.
Picard insists on standing with him in "the First City of the Klingon Imperial Empire", on the continent of Redundant Redundancy.
It's our first look at the storming green skies and baleful surroundings of the Klingon world. It's a nice place to die, but I wouldn't want to visit. You know that song that goes 'might as well go for a soda... nobody hurts and nobody dies?' That's not the case here.
"Your challenge can only result in a fool's death." Kurn declares.
"It is a good day to die, Duras, and the day is not yet over." says Worf. Awesome.
Picard has Data study up on Khitomer while Jean-Luc researches Klingon law.
The Council head K'mpec (apparently of the House of Korrd from Star Trek 5) quietly tells Worf he will lose, and only by leaving now will he avoid shame and death. Duras sends goons to cut'luch Kurn in a dark alley. The cut'luch is an ancient onomatopoeia knife. It does what it sounds like. Picard takes over as Worf's second.
Beverly turns up another Khitomer survivor. Not among the 4000 dead was Worf's badly injured nurse Kahlest. Picard shakes her out of mourning, and in turn she saves him from Duras' hit men. She agrees to be a surprise witness.
The Council was trying to minimize dishonour to Duras, whose family is too powerful to defy. Ja'rod gave the Romulans the defence codes and died with those he betrayed. To protect Kurn and the Empire's "honour", Worf accepts an unjust discommendation. Even Kurn must play along or their might be Civil War. The Council turns their backs on Worf and he can no longer play their reindeer games.
"Sins of The Father" raises a very important question. If your family name is Lorgh, how do you introduce yourself without people handing you Kleenex or asking if you're all right?