When Worf fails to report for duty, Riker goes to his quarters to investigate, finding the Klingon entranced in a ceremonial ritual, oblivious to everything and everyone until Riker's interruption. Concerned because of Worf's developing pattern of sub-par performance, Picard visits him in his quarters. Worf explains that his recent experience in the Carraya sector — from which he brought back some Klingon children — has left him empty inside. He has been trying to summon a vision of Kahless — the greatest of Klingon warriors, who united his people many centuries ago, and promised to one day return and lead them again. Picard grants him leave to visit the planet Boreth, where the Followers of Kahless wait for their leader's return. Worf attempts his ritual again in the ceremonial lava caves. This time, however, a sudden swirl of smoke and light reveals Kahless. Kahless is real — and he has returned!
Worf and the other Klingons, stunned and amazed, follow Kahless into the temple. Koroth doubts it is truly the legend returned, but Kahless then tells them the story of how the Klingon bat'leth sword was forged — a secret that was kept only with the High Clerics in order for them to verify Kahless's existence if he ever came back. This is proof enough for all present except Worf, who later scans Kahless with a tricorder, only to see that the being really is a Klingon.
Kahless and Worf talk privately about the new empire that will form, but Worf discovers some flaws in his hero — Kahless doesn't remember the taste of Klingon Warnog, or what existence is like in the Klingon afterlife known as Sto-Vo-Kor. Later, Worf and Gowron argue over the situation, with Gowron refusing to believe this is nothing more than an elaborate ploy by Koroth and his allies to seize power over the empire, but Worf implores him to open his heart and have faith that this is true. Only Worf's intervention stops Gowron from killing the warrior, but the moment has put doubt in the minds of all.
His heart filled with anger, Worf threatens Koroth later, making him reveal the truth. He and Torin used an organic sample of the original Kahless to create a clone, one in which they imprinted "memories" so even the clone would believe. But Koroth says they still need Kahless — in any form — to help bring together an empire that suffers under Gowron's corruption. Much to Koroth's objection, Worf reveals the truth about Kahless to Gowron, but also expresses the sentiment that their people need a moral leader, someone in whom the Klingons want to believe, to put their faith, and around whom they can rally. Worf suggests that the clone Kahless be made Emperor. Gowron would continue to run the High Council, but Kahless would guide the people and help return them to the honorable ways of long ago. Gowron is given no choice but to go along with this plan. A new era begins, but Worf is still feeling empty, until the clone Kahless tells him it doesn't matter whether or not the original returns, as long as they remember the words he left behind and follow his teachings.