The Earth Saver

From the back cover of the Del Rey first edition: "Tana Winthrop had fought all her life to fulfill the dream of her ancestors: a dream of returning to Earth to learn the fate of the starship Homeward Bound, which had disappeared there centuries before. But when a new technology allowed her to transport herself to mankind's home world, reality turned the dream into a nightmare. For the crew of the Homeward Bound had indeed survived - and gone native. They had an idyllic life on a beautiful, healthy planet and wanted no interference from the star-going civilization that had almost destroyed Earth generations before. But Tana's arrival had reopened the door to the stars, and, once again, Earth was at risk of destruction. Tana was facing the most important battle of her life, and as word of the new technology and the newly vibrant Earth began to spread, she knew that her time was running out. Tana was forced to face the prospect of defeat, unless she found help from an impossible source - legendary hero who had been dead for over two hundred years..."