The final six half-hour episodes of “Tomorrow’s End” continue the story of brother and sister, Petey and Janey Kelly, and their futuristic adventures with the Girl from Tomorrow, Alana, to foil the evil Silverthorn and his plans to use Alana’s time capsule to alter history and destroy the world with nuclear weapons. In the end, the young trio triumph. Alana returns to her world and the Kellys to theirs, but they will never forget their travels together through time.