Humanoid robots known as the Cylons, who were once created by humans but have become their enemy, have been absent for 40 years since a truce was signed. Humans have rebuilt their worlds and live without worrying about the past. When the Cylons reappear with new technologies, they destroy the twelve human colonies with a nuclear holocaust.
The old spaceship Galactica is the only one to resist the attack and becomes the escort for the last surviving humans on the run to find Earth, their original planet.
The Cylons pursue the survivors determined to exterminate them.