Worf's brother Kurn arrives unexpectedly and asks Worf to kill him. He explains that since Worf sided with the Federation against the Klingon Empire, Kurn and his family are outcasts on the homeworld. Having lost everything, he can only regain his honor through the Mauk-to'Vor, a death ritual which only Worf can perform. Worf reluctantly decides to carry out his brother's wish and fatally stabs Kurn, but Dax and Odo burst in just in time to transport Kurn to the Infirmary.
Luckily, Kurn survives, albeit unhappily. Meanwhile, Sisko grows suspicious of Klingon "Military Exercises" witnessed by Kira and O'Brien outside Bajoran space and orders them to investigate. Later, Worf, hoping to give Kurn a purpose on the station, convinces Odo to make him a deputy on his security force.
Kurn takes the job, and initially performs well. Meanwhile on the Defiant, Kira and O'Brien encounter a damaged Klingon ship in the area of the exercises, and the injured crew is forced to request a tow back to Deep Space Nine. Later Worf finds Kurn again in the Infirmary, and discovers that his brother allowed himself to be attacked, hoping to die this way. Odo refuses to work with a man carrying a death wish and fires Kurn. Miserable, Kurn says that his life is in Worf's hands.
While investigating the explosion that disabled the Klingon ship, Worf realizes that it was laying a minefield of cloaked explosives to cut off the Bajoran system from the rest of the Federation — a precursor to war. In order to disable the mines, they need the coordinates. Worf and Kurn have their features and DNA signatures temporarily altered and make their way onto the disabled ship. They soon find the deployment plan for the mines, but a Klingon officer suddenly walks in on them.
Kurn kills the intruder, which shocks Worf until Kurn reveals the Klingon had a knife and was preparing to kill him. But Kurn's act only sinks him deeper into depression as he realizes his dishonor is complete. With this in mind, Worf makes the ultimate sacrifice. He has Kurn's features altered once again and has his memory erased, allowing Kurn to start life over again with a new identity. Kurn has regained his place in Klingon society — but Worf has lost his only remaining link to that society forever.