Forty years after the end of the Cylon War, the artificially-created Cylons declare war on humanity by attacking and destroying the twelve colonies. The military crumbles after their newly updated ships shut down in the face of a new unknown Cylon weapon. A lone Battlestar known as Galactica, due to be decomissioned and converted into a museum, turns out to be the only thing standing between the Cylons and the total destruction of the human race.

With all others in the line of succession dead, Laura Roslin, the Education Minister, is appointed president of the Thirteen Colonies. Her new plan is to round up all of the surviving ships and together with the Galactica flee their home systems, never to return.