When one of NASA's space chimps is thrown off course, he is presumed lost, but has actually been captured by fed-up super-intelligent aliens, given a super-IQ boost, and told he is the new defender of the universe! So he's given his own ship, allowed to select his all-simian crew, and left to fend for himself. Their arch-enemy is the once-powerful Nebulon, an alien composed of stellar matter, who needs the power source from Simian's ship in order to take over the universe.