As Chuck Bartowski continues to come to grips with his newly adopted life as a spy, tension builds between his recently appointed partners Sarah Walker and John Casey. When a doctor who seems to have a solution to Chuck's problem is killed, Casey and Walker turn the blame at one another. Both agents persistently try to convince Chuck that the other one is responsible and now it is up to Chuck to decide which one to trust. Who will he choose?

Chuck faces an unusual task, when Sarah's hot colleague from the CIA shows up requesting help for a mission. Morgan tries to get Chuck to set him up with Sarah's new friend. When Chuck finds out that a million dollar diamond hidden in a Malibu mansion is being used to help fund terrorists, he must help these two beautiful women steal it back. Chuck is finding out that Sarah's job of living a double life, which she is all too good at, is really preventing him from getting to know who she really is.