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.

After the destruction of the Twelve Colonies of Mankind, the last major fighter carrier leads a makeshift fugitive fleet in a desperate search for the legendary planet Earth. This film is adapted from a television series that aired on ABC from September 17, 1978, to August 17, 1980. The first and fifth episodes of the series were edited into this theatrical feature film. Taken together, the two episodes ran 148 minutes, without commercials, while the film runs 125 minutes.