Part 1 of 2. The people of the Twelve Colonies have been at peace with their enemies, the Cylons, for over forty years, but that changes when the Cylons stage a sudden sneak attack that defeats the Colonial defenses and destroys entire population centers under a devastating nuclear attack. The Cylons themselves were created by the Colonials years ago as sophisticated robots with artificial intelligence. Gaining intelligence and consciousness, the Cylons eventually turned on their masters and the first Human/Cylon war was the result. At the time of the sneak attack, the Battlestar Galactica (a space-going aircraft carrier, carrying squadrons of manned fighters as her primary weapon) is being decommissioned and turned into a museum ship. The Galactica fought in the first Cylon War over forty years ago, but has been relegated to peacetime training duties ever since. Her usefulness to the fleet had come to an end and her commanding officer, Adama (Edward James Olmos) was about to be retired. Too far out of position to participate in the initial battle, Galactica ironically becomes the sole surviving battlestar when, through the treachery of a human named Baltar (James Callis), the Cylons gain access to secret Colonial defense systems and are able to annihilate the entire human fleet. Meanwhile, with the death of the Colonial President, civilian authority has been transferred to Laura Roslin (Mary McDonnell), secretary of education and forty-third in the line of succession.