Commander Kurn, a Klingon, is doing an exchange tour on the Enterprise. Kern reports for duty as soon as he gets aboard. Picard tries to keep a straight face, as Kern announces he's going to be harsh on following procedure. Later on, there's a pow wow in Ten Forward - Kern doesn't seem to like anyone. Except Worf. Although up on the bridge, Kern is being dickish toward Worf. Riker suggests to Kern that he might like to pull the stick out of his arse, but the suggestion is ignored. "This is not a Klingon ship." "If it were, I would have killed you for offering that suggestion."
He's also unimpressed by Earth cuisine. "I shall try some of your burnt replicated bird meat!" Wow, they've really gone all out for the dinner. Vases with flowers. And transparent cutlery.
Worf visits Kern in his quarters to ask if Kern doesn't like him, and Kern baits him to the point of rage, then reveals he's Worf's younger brother. He was left at home while Worf and his parents went off to Khitomer and their parents were killed in the Romulan attack, etc. Apparently dad has been judged a traitor who aided the Romulan attack, and Worf needs to defend his honour. If he fails in the challenge, he will be executed. Picard agrees, so long as he can go watch, and the Enterprise sets course for the Klingon homeworld.
So, Worf goes before the Klingon High Council and challenges their judgment. Prepare for much growling and posing. "You come before us wearing a child's uniform." Wow. Maybe if Starfleet uniforms were all creaking leather and stuff... but then it would look like Blake's 7. The Klingon accusing is Duras.
"It is a good day to die." OK, anyone playing a drinking game, take a swig.
Picard returns to the Enterprise and goes into research mode. Klingon way: Hit it. Federation way: Google it.
The council leader, K'mpec, asks Worf to drop the challenge. Then another scene with Riker and co researching. Then a scene where Duras tells Kern he knows Kern is Worf's brother, and sets two other Klingons on him. Kern ends up in sick bay on the Enterprise, but Crusher says he'll be OK. Worf points out if he loses the challenge, Kern will be executed anyway.
Data finds that recent records were recovered from a Romulan ship, which indicate that there was a transmission from Khitomer. They compare the logs with those from a Federation starship which was in range, and Geordi points out that they've been quite obviously tampered with.
Worf angsts over the fact that he can't use Kern as his cha'Dlch, and asks Picard to do it instead. They return to the challenge, and the other Klingons are not impressed by Worf's new pink and squishy cha'Dlch.
Riker and co find that there was another survivor of Khitomer, a woman called Kahlest. Their Google-fu is strong. They let Picard know, and he asks for another recess. Worf says that Kahlest was his nanny.
Picard locates Kahlest, now an old woman, who refuses to help because Klingon culture has eschewed her for not dying with honour. Picard steps outside and is set upon by two Klingons, one of which he kills, but the other pins him and prepares to take the killing blow. Kahlest kills the other. She agrees to return with him, and they burst in just as the pronouncement is about to be made.
K'mpec and Duras realise they're beaten, and admit that it was Duras' dad who was the traitor, but his family is powerful, and the revelation would cause problems for Klingon society. K'mpec says Worf's challenge cannot be allowed to succeed, prompting Picard to give an enraged speech. Worf offers to give his life for the empire and, after some haggling, Worf offers his discommodation. And slaps Duras about a wee bit.
Kern is annoyed, but Picard says that there will be another day on which they can prove his dad's innocence. Plus he can use this to blackmail K'mpec for favours. So Worf is excommunicated. The End.
Not bad for a Klingon episode...