When the initial Cylon attack against the Twelve Colonies fails to achieve complete extermination of human life as planned, twin Number Ones (Cavils) embedded on Galactica and Caprica must improvise to destroy the human survivors.

The number One Cylon brothers Cavil organize a massive coordinate simultaneous attack to destroy the twelve colonies, but it fails to wipe out human life or break the human spirit. They now orchestrate deceptive actions, infiltrating surviving communities, notably aboard flagship Battlestar Galactica and Samuel Anders's human trainees class on planet colony Caprica. Both sides must confront existential as well as pragmatical challenges to battle for survival.