Just when Toller Maraquine II - grandson of the hero of "The Ragged Astronauts" and "The Wooden Spaceships" - thinks that life on the twin planets of Land and Overland has become dull and boring, and that the adventurous times of his illustrious ancestor are gone forever, he discovers a rapidly growing crystal disk, miles in diameter, creating a barrier between the two worlds. Armed only with his sword and boundless courage, Toller goes to investigate, unaware that he is about to decide the future of entire planets and their civilizations.