Synopsis: "New technologies create new and unexpected hazards. In the not-too-distant future, humanity has developed a faster-than-light engine, and has begun to explore the first 200 hundred light years in every direction from Sol. Planets discovered and cataloged in the previous century are investigated using the new engine. Additional worlds in radical locations are discovered as the first and second waves of explorations are sent out from Earth. Some of the worlds are habitable by humans, and some of the worlds bear evidence of visitation in the distant past by a species the explorers call Nelf. Nelf objects that remain on these worlds are impossible to understand and may or may not be functional. No signs exist to indicate the fate of the Nelf in the time between their last activity on these worlds and the arrival of humans." — quoted from this book's product page on Amazon as of 2018-02-07.