Before the first animals showed up on Earth, immortal incorporeal aliens crash-landed on our planet. They’ve been trying to get back to their own planet ever since. Their strategy has been to promote the intellectual and technological development of the most promising animal species they could find — humans. They do this by inhabiting certain promising humans and guiding their thoughts and actions. They knew it would take thousands of years, but someday they will direct humans to create the spaceships they need to get home.