Sydney discovers a link to her missing two years in the form of Simon Walker, the dangerous and sexy leader of a group determined on retrieving deadly biological weapons. Meanwhile, Vaughn struggles with his own feelings of jealousy and longing while Sydney is on her mission, aware of the pressures his job is putting on his marriage to Lauren. Jack takes matters into his own hands to protect his daughter, purposefully revealing Sydney's deadly secret to Dixon in order to preserve her position inside the CIA.