A Magic School Bus Halloween is a Halloween special based on the PBS Kids series The Magic School Bus, originally aired on October 31, 1995. It features both live-action and animated segments. In class, the students rehearse for the musical with each different student playing a different instrument. Ralphie is on the xylophone, Phoebe is on the saxophone, Arnold is on the sousaphone, Tim is on the violin, Keesha is on the clarinet, Liz is on the drums, Wandais on the trombone, and Carlos has a special instrument he invented himself, with Dorothy Ann as the music conductor. When Carlos plays his instrument, it elicits dissonance and fails to complement the orchestra. Ms. Frizzle then comes around wearing a costume with various of instruments. She takes off the costume and the class tell her about Carlos' instrument, which is devoid of harmony, and the rehearsal at thesound museum is this afternoon.
Ms. Frizzle leads the class to The Magic School Bus and the classtake a ride. Carlos decides to put a blue top hat on the instrument to make it sound better, which proves to be futile. When Carlos says that he need more time, Ms. Frizzle alters The Magic School Bus' speed and iteventually breaks down. Ms. Frizzle exits the bus and takes in temperature before she finally concludes that The Magic School Bus is overheated, telling the class they will be stuck in the woods for a while, which gives Carlos enough time to work on the sound of his instrument, only for Dorothy Ann to worry about missing the rehearsal.
When night falls, the students have to push the bus uphill while Ms. Frizzle hauls it. They stop when they hear a sound. Carlos had put an umbrella on his instrument to have a thunder sound to it, as well as amane to sound like a lion's roar. Dorothy Ann rebuffs those decisions, telling him that the thunder sounds more like a drizzle and the mane sounds more like a kitten.
As the students continue to push The Magic School Bus, they hear another sound. They think that it was from Carlos' instrument. But Carlos denies this, and the student view a house. They walk to it and Carlos says that it's kind of "eary". When Ms. Frizzle rings the doorbell, which makes a peculiar sound, Arnold, Ralphie, and Tim decide to leave. But Carlos wants to know what made the sound. So the students reluctantly enter the house and the door makes a loud sound as it shuts.
Inside the house, the students search through the house for a phone. When Ralphie discovers that the doors are locked, Ms. Frizzle says "hello" in a loud voice. Her echo travels through the hallways and Ms. Frizzle says that it sound friendly enough. Dorothy Ann finds a phone book and the others hear the phone ringing. Ms. Frizzle picks a book off the shelf, which blows a foghorn when flipped open. Carlos thenconcludes that the books were making the sounds and Ralphie turns to leave, only to trip over a book. Ms. Frizzle then shows the class a picture of Professor Cornelia C. Contralto, eccentric collector of sounds, born in the year 1807 and disappeared in 1892. Ms. Frizzle then tells the students that after her disappearance, the house turned into asound museum, which is confirmed Dorothy Ann's prediction that the class missed the rehearsal. Ms. Frizzle also explains that Professor Contralto devoted her life towards sound and her whereabouts are obscure. Ralphie surmises that Professor Contralto is a ghost seeking for the perfect sound. Ms. Frizzle also tells the class that they would be spending the night, much to Arnold's fear. When Tim steps on a panel,the class comes across a rotating wall, which propels them to an adjacent bedroom replete with ample beds.