The Plan takes place during the events of the original Battlestar Galactica series, focusing on the actions of the Cylons during the initial attack on the Twelve Colonies. The story is told from the perspective of two Number One models, Cavil, who are embedded within the human society and the crew of the Galactica.
As the Cylon attack begins, the two Cavils work to sabotage the human defenses from within. However, their efforts are ultimately unsuccessful, and the human fleet manages to escape.
Following the attack, the Cavils continue to work towards their mission of wiping out the remaining human survivors. However, as they observe the humans and their actions, they begin to question the validity of their mission and their own existence.
The film also chronicles the experiences of several key characters from the original series, providing new insights into their motivations and actions during the early days of the conflict.
As the story unfolds, the two Cavils must confront the consequences of their actions and reconcile their loyalty to their own kind with their growing respect for the resilience and determination of the human race.