Time snakes between alternate universes. Ever watchful, an alien intelligence survives on Mars, waiting to be found by spacefarers from Earth. The alien's ultimate goal is to send human astronauts back in time, where they will alter the past and thwart the extinction of the dinosaurs. A race of intelligent dinosaurs, resembling the alien's extinct species, subsequently evolves to rule the world. But a human female astronaut, through a strange twist of fate, survives the change in the space-time continuum. After finding herself in a dinosaurian body, she must race against time - and the formidable alien - to restore the universe to its rightful course.