In the main plot of the show, the [[Cylons]] return to fight the human race. However, the [[Cylons]] have evolved - or developed themselves - to appear human. Using various sleeper agents, they permeate the Twelve Colonies and bring about a massive surprise attack, leaving only around 40,000 humans alive. | In the main plot of the show, the [[Cylons]] return to fight the human race. However, the [[Cylons]] have evolved - or developed themselves - to appear human. Using various sleeper agents, they permeate the Twelve Colonies and bring about a massive surprise attack, leaving only around 40,000 humans alive. |