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.

Chuck accidentally runs into a fellow government agent who seems to be living a similar life. It turns out this agent is a gadget whiz, whose brain makes him a national security asset and a dangerous liability, much like Chuck. Chuck faces a predicament whether he should help turn this agent into Sarah and Casey or help this agent escape his handlers. Meanwhile, Halloween, a holiday that means a lot to Chuck and Morgan as buddies, proves to be a little different this year as Morgan feels that Chuck is neglecting both their childhood and friendship.