Worf prepares to accompany Dax and Kor, a legendary Klingon warrior, on a mission to recover the Sword of Kahless, the mythical, millennium-old weapon of the Klingon Empire's first leader — an artifact missing for centuries. When the drunken Kor finally retires to his quarters after first speaking with Worf, he is attacked by a Lethean, who reads his mind, then erases the incident from Kor's mind. The next day, Sisko — hoping to restore Federation/Klingon relations — allows them the use of a Runabout for travel to the Gamma Quadrant world where the Sword is believed to be located. Upon arrival, the three get into a deserted, protected chamber, but find that all the artifacts hidden there have been removed.
Kor is crestfallen. But Worf, unwilling to give up, discovers another hidden chamber, where they finally find the Sword of Kahless. They prepare to depart, but are met by Toral, a Klingon enemy of Worf's, with four soldiers and the Lethean. A fierce battle for the Sword ensues, and while Worf is wounded, the three manage to escape with it into a cave-tunnel and trap their adversaries in the chamber. Once free, they discover that contact with their Runabout has been blocked — they'll have to make their way to the surface on foot for a chance to transport off the planet.
As they travel, Kor begins to feel contempt for Worf, dismissing him as "too human." Worf also becomes less-than-enamored with Kor, especially when Kor hints that he will not present the Sword to the emperor as planned — he will use it to unite the Klingons himself! Later, Worf decides that it is his destiny, not Kor's, to possess the Sword and lead his people.
The seemingly-endless journey takes the three of them to an abyss, where Kor slips and loses his footing, but still holds the Sword. Worf saves Kor by grabbing the other end. Straining, he tries to convince Kor into letting go and landing on a dangerously small ledge, but Kor refuses. Finally, Dax has to intervene and help pull up Kor. Tired of their fighting for possession, she insists on holding the Sword for the remainder of the trip, even while she sleeps.
Dax is awakened by the sound of Worf and Kor, ready to fight to the death. Suddenly, Toral, the other Klingon warriors, and the Lethean attack, but the three are able to defeat them, Kor wielding the Sword — which seems to make him invincible. Then, Worf and Kor turn on each other, and Worf is on the verge of killing Kor when Dax stuns each of them with her phaser, then transports the three of them back to the Runabout. Later, onboard, Worf and Kor realize that the Sword turned the two against each other, and will probably divide the Klingon people as well. Because of this, they transport the Sword into space, hopefully not to be found for at least another millennium, when the Klingons may be ready for it.