When a secret government neural computer called the Intersect is stolen, NSA agent, Colonel John Casey (Adam Baldwin) is sent to Burbank to retrieve it. He is teamed with CIA agent Sarah Walker (Yvonne Strahovski) and together they discover that the Intersect has been downloaded into the brain of a civilian, Chuck Bartowski (Zachary Levi). Chuck leads an uneventful life working as a computer geek at the Burbank Buy More.
When it becomes obvious that the Intersect can't be recovered, Casey and Walker join forces to protect and work with Chuck in their ongoing battle against assassins, terrorists, and general bad guys, including a secret spy organization called the Ring.
A by-the-book former soldier, Casey goes undercover as a retail salesman at the Buy More to keep tabs on his charge. Reluctantly, he becomes a mentor and friend to Chuck as they go on dangerous missions with Sarah.
Alexander Coburn was John Casey's real name. When he was only 23, he was recruited into the NSA by Ty Bennett (Carl Lumbly) his instructor. Believing in his duty as a soldier, Coburn faked his own death, leaving behind his fiancée and assumed his new identity, John Casey. He did not realize that his fiancée was pregnant at the time. Years later, when Bennett returns, Casey feels obligated to help his former instructor on one last mission. Unfortunately, it results in Casey being fired from the NSA for treason.
No longer an agent, Casey wonders if there is more to life and decides to re-enter his daughter's life. Eventually, Chuck and Sarah help him get his old job back at the NSA and he tries to reconcile his new duties as father and friend.
"Weap-Con, the greatest weapons convention. I go every year. I find it very relaxing. It looks like this year, I'll be able to write it off as a business trip."
"That's an understandable mistake. One of them looks like a spy and the other one looks like Chuck."