The relative calm of Deep Space Nine is shattered by the arrival of three aged Klingon warriors — drunken, overweight Kor; warlike Koloth; and their leader, Kang. The three came to find Curzon Dax, and are surprised that he is no longer alive. Kor has no problem adjusting to Dax in her new, female form, while Koloth scoffs at the idea that she was once his old friend Curzon. However, Kang has the most trouble accepting Jadzia, because he has come with a mission. The group's greatest adversary, a man known as the Albino, has been located, and the foursome can now fulfill the blood oath they made decades ago to kill him.
Dax is unsure of whether or not she can go through with the oath that Curzon made. Kang reminds her that as a Trill, she has no obligation to fulfill what her symbiont promised. Still, Dax knows that a Klingon blood oath can never be broken, and confused, she seeks Kira's advice, telling her the story of how this began. After the Klingons were victorious over the Albino, he murdered the firstborn sons of Kor, Koloth, and Kang. The three took a blood oath of revenge, and Curzon Dax, as the godfather to Kang's slain son, took one as well. Compelled to keep that oath, Dax visits Koloth in a holosuite and engages in battle with him, successfully holding her own and winning his support. However, Kang still refuses to let Dax participate.
Dax meets with Kang and uses Curzon's deep understanding of the Klingon race to force him into changing his mind. However, while Kang agrees to let her go, Sisko, who has learned of Dax's plan from Kira, does not, and reminds her of her duty to Starfleet. Dax tells him that she will still go, and is ready to face the consequences when she returns — if she returns.
The foursome travels to the Albino's world, and almost immediately, Dax and Kang clash over the best course of action — Kang wants to march up and fight the Albino in full view of everyone, while Dax believes a more clandestine course of action would be more appropriate. Meeting privately, Kang admits to Dax that the Albino actually invited him, giving the aged warriors a chance to die with honor. Dax suggests it would be better to win with honor, and proposes a plan to increase their advantage. Kang, newly impressed, agrees to go along.
The group puts their counterattack into effect, surprising the Albino in his command post. The Klingons perform admirably despite their age, defeating the guards before Koloth is killed and Kor wounded. Kang is mortally wounded and falls to the ground, but Dax is then able to disarm and corner the Albino. Faced with the opportunity to kill him, she hesitates, but Kang is able to summon the last of his strength and deliver the death blow himself before dying. After bidding farewell to Kor, Dax returns to the station, a different person after her experience.