"Rightful Heir" told the story of the Klingon messiah, Kahless the Unforgettable. In "Rightful Heir," we learned that at the end of his worldly life, the great Kahless pointed at a star in the heavens and promised to return one day. Centuries later, Klingon clerics built a monastery on a planet orbiting that star. Those clerics, impatient for Kahless's return, created a clone of the messiah, using an ancient sample of dried blood. Worf made a pilgrimage to that monastery and helped unravel the mystery of the new Kahless.