After multiple expeditions to other worlds in our solar system, and multiple encounters with other forms of life, Earthmen find a new specimen on Saturn's moon, Titan.; An explorer finds a planet very similar to Earth except for some distinct differences. Attempting to bring its inhabitants technology from Earth, the explorer runs into roadblocks at every turn, until he sees the light.; The Kull are a peaceful people who have discovered random "anti-matter blotches" throughout space. In order to warn travelers about the blotches, they've stationed "lighthouses" in their vicinity. One of the lighthouses loses its position and drifts into our solar system. Two earthmen investigate the lighthouse and become prisoners when the lighthouse is retrieved by the Kull. They find themselves caught up in a gambit between the Kull and their enemies, the Zarran.