Summary:

Edward James Olmos ... Admiral William Adama
Mary McDonnell ... President Laura Roslin
Jamie Bamber ... Captain Lee 'Apollo' Adama
Tricia Helfer ... Number Six
Katee Sackhoff ... Captain Kara 'Starbuck' Thrace

The Cylons declare war on humanity wiping out billions in an unprovoked first strike. The Colonial fleet is all but eliminated leaving just a handful of ships including the soon to be decommissioned Battlestar Galactica. Galactica is crewed by the misfits of the military and a crew that never expected to be involved in real duty. With the president gone, and the government all but eliminated Laura Roslin, the Education Minister takes on the mantle of President of the 12 Colonies.

Gaius Baltar, the leader in Artificial Intelligence, has inadvertently betrayed humanity by allowing a Cylon agent into the defence network rendering it, and all of their military forces impotent in the face of the Cylon attacks. During his time with this agent, it has implanted a chip into his brain allowing it to speak to him, and continue to torment him. Over the season Baltar falls in love with the Cylon eventually betraying humanity again and again.