It looked like an ordinary bunny to Harold. But Harold was a dog by profession, so his judgement wasn't reliable -- as he was the first to admit. But Chester, Harold's good friend and house-mate, was a very well-read cat and he knew there was something strange about Bunnicula. For one thing, he seemed to have fangs. And the odd markings on his back looked a little like a cape. But when Chester started finding white vegetables, drained dry, with two fang marks in them, he was sure Bunnicula was a vampire bunny.
So it was up to Chester -- with Harold's help -- to alert the members of their household before another carrot was lost. Because as Chester warned, "Today vegetables, tomorrow the world!"