The fates of all three of Firestar's grandchildren are linked by a mysterious prophecy, but only one of them - Sparrow - knows about it. He feels an irresistible desire to go to the distant mountains, where, as he believes, he will be able to learn not only about the prophecy itself, but also about the fates of the ancient cats that once lived by the lake - Cliff and Leaffall. Hollypaw and Lionpaw also really want to see the world, and when representatives of the Falling Water Clan turn to the Thundercats with a request for help, all three are given such an opportunity, although it is a matter of life and death...