SAN DIEGO — The Walking Dead isn’t really about zombies. It’s about how ghoulish people can become in the face of a zombie takeover, according to the show’s stars.

At the onset of Season 2, Walking Dead’s heroic lawman Rick Grimes is facing his own struggles with humanity and his need to protect his family, says Andrew Lincoln, who plays Grimes.

“Do you survive at all costs and lose your humanity b...