S4, E18: Chuck and Sarah investigate when they suspect that Casey is carrying out private missions. Meanwhile, Chuck fears that the CIA's seemingly perfect new operatives (recurring guest stars Isaiah Mustafa and Stacy Keibler) will render him obsolete. Elsewhere, Morgan settles in with a new roommate and Awesome panics when Ellie embarks on a potentially dangerous line of research. Recurring guest star Robin Givens also appears.