Much like in Hair-Raising Hare, Bugs (after being flooded out of his rabbit hole while sleeping during a heavy rain) finds himself trapped in the castle of an "evil scientist" (the neon sign outside his castle says so, punctuated with a second flashing line, "BOO"), who this time is a caricature of Boris Karloff and needs the rabbit's brain to complete an experiment. When Bugs awakens, he is terrified when he sees the scientist ("Eh, eh, eh, w-w-what's up, doc?"), a sarcophagus ("What's going on around here?") and the robot experiment ("Where am I anyway?"), eventually running away upon seeing all three. The scientist sends out a big orange monster wearing a pair of sneakers (here called "Rudolf") to retrieve him, with the promise of being rewarded with a spider goulash.
Bugs keeps running until (in a scene very similar to one in Hair-Raising Hare) a door on the floor opens and a rock falls into a water pit where there are crocodiles swimming around. While he is walking backwards and praying to jump over the crocodiles, he bumps into Rudolf. Bugs comes up with an idea ("Uh oh. Think fast, rabbit!") and makes as a gabby hairdresser, giving the hairy monster a new hairdo ("My stars! Where did you ever get that awful hairdo? It doesn't become you at all. Here, for goodness' sake, let me fix it up. Look how stringy and messy it is. What a shame! Such an interesting monster, too. My stars, if an interesting monster can't have an interesting hairdo, then I don't know what things are coming to. In my business, you meet so many interesting people. Bobby pins, please. But the most interesting ones are the monsters. Oh, dear, that'll never stay. We'll just have to have a permanent.") He gets some dynamite sticks and places them in the monster's hair, which give the appearance of curlers. He lights them and runs off just before the explosion ("Now, I've got to give an interesting old lady a manicure; but I'll be back before you're done."), which leaves Rudolf with a bald head.
Rudolf realises he was tricked and goes after Bugs. In the chemical room, Bugs sees vanishing fluid and he pours it all over himself ("Mmm, not bad!"). Bugs gets a trash can and dumps it on Rudolf. Then he gets a mallet and hits the trash can causing it to shake, and pulls out the rug Rudolf is standing on from underneath his feet, causing him to fall on his bottom. For the coup de grâce, Bugs takes a bottle of reducing oil and pours the entire contents over Rudolf, who lets out a roar and shrinks. Putting on a suit, coat and hat and grabbing two suitcases, Rudolf enters a mouse hole, kicks its resident out and slams the door which bears a sign saying "I QUIT!" The mouse says "I quit too", holding up a bottle of whiskey ("xxx"), then dashing away.
Bugs eats a carrot in satisfaction of getting rid of the monster ("Well, that's that."). Suddenly, the mad scientist restores him with "hare restorer" ("Never send a monster to do the work of an evil scientist"), insisting the rabbit hand over his brain ("Now be a cooperative little bunny, and let me have your brain"), throwing an axe straight towards Bugs (who doesn't want the scientist to have his brain, stating "Uh, sorry doc, but I need what little I've got"), who ducks. The axe breaks open a large bottle of ether which drugs Bugs and the scientist. The groggy scientist ("Come...back...here...you...rab-...bit") chases after an equally groggy Bugs in slow motion (Carl Stalling cleverly punctuates the chase by playing a slow but "drowsy" version of the William Tell Overture). Bugs trips the scientist, who falls asleep.
Bugs runs slowly out of the castle and over the horizon, tripping over a rock and falling asleep, landing in a stream which leads Bugs straight back into his flooded hole. He suddenly wakes up and declares that it must have been a nightmare. The miniature Rudolf suddenly passes by on a rowboat and tells him in a high-pitched voice: "Oh yeah!? That's what you think", leaving Bugs with a confused look on his face.