The crew of the *Challenger* were in an agonising situation: they had been born on their starship and had never set foot on a planet, and yet the Earth was their spiritual home. For years they had studied holograms and videos of Earth in the *Challenger's* library, and had dreamed of the time when their ship would return so they could walk under the Earth's blue skies, feel warm summer breezes on their faces, and cool green grass beneath their feet. And now the Earth had vanished from their solar system. From clues discovered on the abandoned colonies of the other planets they learned that the people of Earth had taken their planet in search of a new sun--a sun that was not liable to become a nova. The crew decided to go in search of their lost planet. Even though the trail was half a million years cold...