From the introduction:
It is the Year 204 After Abduction, and the humans on Xantus number about 5,000. They all live in a partially underground structure called the Den, built from part of Ship, which is still controlled by a sapient but usually uncommunicative computer, also called Ship. The player characters must use good old human ingenuity, the products of backengineered alien technology, and special abilities called “Flukes,” which have evolved in response to the alien microbes and extreme evolutionary pressures suffered by the generations since capture, to explore Xantus, defend the inhabitants of Den, and try to divine the nature of the Abductors and why they brought humans to Xantus.
The game document includes the game rules, the distinctive campaign setting, and an introductory adventure.