“Sons of Mogh” is episode fifteen of season four of Star Trek: Deep Space Nine.
Worf’s brother Kurn (Tony Todd) arrives at DS9. He wants Worf to help him with a Klingon ritual. When Worf refused to help Gowron in “The Way of the Warrior: Part 2”, the House of Mogh was stripped of all its lands, ships and its seat on the Klingon High Council. Kurn has lost his honour, and wants Worf to help him regain it. The ritual involves Worf killing Kurn.
Dax figures out what is happening and, although Worf performs the ritual, Kurn’s life is saved. Captain Sisko is not happy about the Klingon rite being performed.
Whilst on their way back to the station. Chief O’Brien and Major Kira detect something odd just outside Bajoran space. A Klingon Bird of Prey decloaks and tells them to leave.
Worf has to figure out what to do about his brother, and Sisko has to determine what the Klingons are doing.