As Halloween approaches, two new series stray deep into "Night of the Living Dead" territory, and both deliver some soul-shriveling scariness. But only the best of them can take a theme as familiar as a zombie apocalypse and make a moving drama that also feels shiny and new. So what if we, like many of the characters, are brought repeatedly to the edge of a terminal existentialist funk? Summon the will, as they do, to tough it out until the nightmare ends—and the thrill is palpable.

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