As part of an exchange program, a Klingon officer named Kurn arrives on board the U.S.S. Enterprise. He soon informs Worf that they are brothers, having been separated shortly before their parents were killed in a Romulan attack on the Khitomer Outpost.
Kurn tells Worf that new evidence has surfaced which indicates that their late father, Mogh, aided and abetted the Romulans in the Khitomer assault which resulted in the deaths of 4000 Klingons. To defend his family's honor, Worf goes before the Klingon High Council to challenge the treasonous accusations.
Accompanied by Kurn, who serves as his brother's cha'Dlch (a second who will defend him during the trial), Worf faces the high council. During a recess, the council leader, K'mpec, asks Worf to drop his challenge, but he refuses. Elsewhere, Kurn is seriously wounded by two Klingon assassins after Duras, another council member, requests that he betray Worf and Kurn refuses.
Due to Kurn's injuries, Worf asks Picard to be his cha'Dlch. Honored by the request, Picard returns to the council with Worf. Meanwhile, the crew learns that Klingon records of the fatal attack have recently been altered to indict Mogh and that the only other survivor of the massacre, Worf's nurse Kahlest, is living nearby.
Picard visits Kahlest, who asserts that Mogh was loyal to his race and had actually followed the real traitor to the Khitomer Outpost to prevent the Romulan attack. But when Picard tries to introduce Kahlest's testimony, K'mpec abruptly cuts him off and calls a recess before she can prove Mogh's innocence.
In private chambers, K'mpec admits that Mogh was a scapegoat for the real traitor, Duras' father, to protect political interests and prevent a civil war. He also reveals that the council never expected Worf to challenge their charges, but since he has, he must be punished for his father's "treason" to keep the peace. To protect Kurn, who would face execution along with him, Worf agrees to drop his challenge and instead be labeled a coward before the council, though in their hearts, Kurn and Worf know that their family honor has been maintained.