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.

As season 4 begins, the last remnants of humanity continue their search for a new home. Galactica’s crew attempts to make sense of the inexplicable while four members of the fleet are still reeling from past revelations.