Plot summary
Lt. Worf fails to report for duty, and Lieutenant Commander Data and Commander William Riker become concerned. Riker finds Worf's quarters filled with incense and burning candles while his chief of security sits before a small fire in a trance-like state. Worf later explains to Captain Picard that he was attempting to reconnect with his Klingon spiritual beliefs by summoning a vision of Kahless, the messianic warrior who founded the Klingon Empire. Picard suggests Worf immerse himself in Klingon culture, granting him leave to journey to the Temple of Boreth.
After ten days of doubt-filled rituals, Worf is approached by a physical manifestation of Kahless. Worf brings the prospective spiritual leader to the Enterprise, but is troubled that Kahless does not remember how Klingon warnog tastes or what Sto-Vo-Kor, the Klingon afterlife, is like.
Klingon Chancellor Gowron arrives with a test to prove whether Kahless is genuine. Gowron is displeased with the prophet's return, convinced he is an imposter foisted by the priests to gain power. Gowron requests that the Federation genetically test the dagger he brought, stained with the blood of Kahless in antiquity. The test indicates a match.
Gowron provokes a D'k tahg duel with Kahless and wins, leaving Worf to ponder how the "greatest warrior of all" could be beaten. Worf confronts Koroth, High Priest of the Boreth Temple, who admits that Kahless is a clone of the original, noting that the legend of Kahless' return did not specify the exact manner. He feels Kahless is needed to rally the people's faith. Data advises Worf that during a crisis of his own, he made a leap of faith to assume he could evolve beyond the sum of his programming.
Gowron is outraged when Worf tells him the truth and prepares to execute the clone and priests. Worf tells Gowron he supports Kahless, explaining that he made a leap of faith. He suggests the Klingon High Council appoint Kahless to the ceremonial position of Emperor; while only a figurehead, he might unite the Klingon people. Seeing the wisdom of cooperation, Gowron offers his devotion. Departing for the Klingon homeworld Qo'noS, Kahless notes the troubled demeanor of the "Son of Mogh " and reassures him that the beliefs espoused by Kahless made the ancient Klingons what they were; his spirit lives within the hearts of all true Klingons.
Credits
Adapted from Wikipedia contributors, Rightful Heir. Paragraphs and formatting adjusted; illustrations, reference markers, block quotations and non-story material omitted.