Bedlam Planet

Everything about the planet revolving about Sigma Draconis seemed to indicate that here was a world that could be made into a second Earth. It was fertile and lacked native inhabitants and dangerous beasts. Then what was troubling the pioneer colony that had landed and set up shop there? Was it really possible just to create a new Earth on any vacant world waiting a landing? . Or was there a lot more to planetary ecologies than humanity realized?