When the ancient enemy the Cylons appears and destroys the 12 colonies, the crew of the Battlestar Galactica sets out to protect a small fleet of civilians, the last of humanity, on the journey to the 13th colony, Earth.
The source of Galactica's power is under danger. As all is going on, Starbuck gets hurt at a hospital on Caprica, raising questions about her doctor's hidden intentions.
In this season, the enemies of the human race, the Cylon army, manage to take control of the planet New Caprica, which includes a human colony, while Ellen does her best to release her husband.
The aftermath of a coup between the Cylon family leads to more violence, while Cally learns the shocking truth about her husband.