The Celery Stalks at Midnight is third book of Bunnicula Series.
Bunnicula has gone missing and Chester begins to fear for the town again. This time, he believes that the vegetables that Bunnicula sucks dry could return as the rabbit's vampire slaves, which he will then use as an army to take over the town. Armed with a box of toothpicks to stab through the "hearts" of vegetables, he, Harold, and Howie set off to search the neighborhood for white vegetables. After some success, they witness Toby and Pete wearing dark robes and holding a group of frightened children prisoner. The pets fear that Bunnicula has begun to take over people as well and run to the nearby school, which is full of what they suspect are the rabbit's servants.
After causing much mayhem (including Chester destroying a large white carrot, which he believes is the head of the undead vegetables), they are caught by the Monroes. It is revealed that there was a carnival at the school that day, and Toby and Pete and the other children were rehearsing for a play they were going to put on. The "carrot" that Chester destroyed was actually a carrot cake, shaped like a carrot and covered in cream cheese. Finally, Bunnicula was found at the school, entered in the pet show. The pets find out that Bunnicula spent the previous night in the garage, which was accidentally left open, which meant he did indeed leave the house to feed on vegetables.
At the end, Edgar Allan Poe's "The Tell-Tale Heart" is parodied when Chester finds an artichoke heart under his favorite chair. After telling Chester there's nothing to worry about and trying to fall asleep, Harold hears a faint thumping.... he opens his eyes to find the vegetable in question right in front of his nose, which leads him to ask if Chester has a toothpick handy. It is left ambiguous as to whether or not this is a prank by Chester, or an actual attempt at a vampiric attack on Harold by the artichoke.