A motley crew of explorers (two human, two alien) is sent to the mysterious ring world to find out if the unknwon, yet unbelievably advanced Ringworld Engineers who built the place are friendly. Unfortunately, their spacecraft crashes and leaves them stranded on what seems to be a mostly deserted world, whose inhabitants are few, far in between, and, having devolved back to a pre-technological stage, unable to help them to get back home.