At its core, "Homeland" has always been first and foremost a show about two characters: Nicholas Brody, the heroic POW who fell under the sway of his captor, Abu Nazir; and Carrie Mathison, the bipolar CIA officer whose unpleasant personality makes her really good at her job. For all its increasingly loony plot twists, the show has stayed true to those characters, allowing them to evolve in mostly believable ways and bringing them together in a mostly swallowable fashion.