You got to find it to stop the bad guy, repair the universe, or destroy it once and for all. Rightful rulers - a race believes that they've been taken, and that the world rightfully belongs to them. Stowaway - You just got away from the bad guy and saved the universe. Strangers in a strange land - figuring out what's going on is in and of itself an adventure. Survival - A species or race reduced to its last nubers fights desperately for survival in a hostile environment.
Science becomes the work of the gods, is shunned or is enshrined as law or procedure.
Technology gone wrong - advanced coputers or robots begin to think for themselves, and they don't see why they're keeping these messy humans around. Things from another dimension - revenge for imprisonment, megalomania, xenocidal, or confused and deadly creatures from somewhere man was not meant to mess with come here for a visit. You're the bouncer. Traitor - Your trusted companion turns out to be an ally of the bad guy. Look out, just when you think you've won the day - someone turns on you.