"Gets a Bright Idea" is the fifth episode of season three and the thirty-first episode overall of the animated children's series The Magic School Bus. It originally aired on October 12th, 1996.
Arnold's cousin, Janet, was disappointed by the all-school field trip to a light show, as she wanted to see a magic show. She tells the class she could do a magic trick, but she can't because of the ghost that haunts the theater. When they leave, they find Arnold missing. When they enter again, they see his "ghost". Keesha, the skeptic, is convinced that it is really a trick done by Janet to scare them.
At the theatre, the class is watching a light show, which Janet finds boring. After the show, Janet dismisses the show and claims to make real magic with light. When asked by Keesha to do so, Janet claims that she can't due to the ghosts in the theatre. She tells the class that the ghost would get them once all of the lights turn out. But Keesha scoffs at this, stating that ghosts don't exist. Janet tells her ghosts don't like when anyone says that and puts the blame on Keesha if anything terrible happens to any one of the kids.
The class run out of the theatre on fear and notice that Arnold and Janet are still inside the theatre. Ms. Frizzle then arrives in her bus wearing a light-up dress. When the class inform Ms. Frizzle of Arnold's absence, she guides the class back inside the movie theatre and they go on an exhaustive search around. In the dark, Ms. Frizzle turns on her light-up earrings and the class go inside the main theatre where they find a source of light on the stage, which Ms. Frizzle calls a ghost light, something the last person who leaves the theatre turns on (which Dorothy Ann reads in her book). The class continues to search for Arnold and someone pulls the plug, turning off the ghost light. The class then become shocked once they view what appears to be Arnold's ghost hovering over them.
The class becomes convinced that the ghost really did get Arnold and Arnold's "ghost" dissipates gradually once the light comes back on. When Ms. Frizzle turns out the light of her earrings, Keesha learns that it's hard to see anything without the light. Ms. Frizzle turns the light of her earring back on and Keesha tries to garner the facts after the light show. The last time Arnold was seen was when he was with Janet and Janet became annoyed that the class didn't attend the magic show she wanted to go to. So Keesha surmises that the whole illusion was implemented by no other than Janet herself just to scare the rest of the class, but the rest of her class (except Phoebe, sort of) disagreed with her. Keesha also adds that there needs to be more light around the theatre to see through the dark corners to prove that it's only an illusion. So Liz brings a bus with a giant light bulb on top inside the stage and adds a light tube. Keesha hops inside, travels inside the light, and ejects out of it. The other class follow suit and eject out of the bulb in different directions. Ms. Frizzle explains to the class that light from different source all do the same thing as well. Keesha also learns that the light travels in straight lines away from its source and that the class should aim the light in one directipon to get it into the dark corners on top to find Arnold. Ms. Frizzle brings out a mirror and Liz hops into the bulb and ejects out of it, bouncing off the mirror in the process. She lands on one of the levers below her and she, Tim and D.A. take a ride through a trapdoor. Keesha comes across an old footlight with a candle inside that Ms. Frizzle lights up. Wanda notices that the metal bowl around the candle keeps the light from spreading out, bounces the light back, and aims it at only one direction, similar to how the mirror did to Liz. So Carlos decides to use an even bigger footlight and the class light it and put in on top of the bus to shine it on the direction they want it. The class then notices Liz, Tim and D.A.'s absence.
The three are inside a basement and find a bunch of junk and D.A. shines a flashlight (given to her by Liz) to a tree. When she notices its shadow, D.A. learns that light travels in straight lines and doesn't go around any objects, but rather bounces off them, thus creating a shadow.
Meanwhile, the class continues to search for Arnold and finally gets a glimpse of his glasses floating in midair. When Ms. Frizzle shines the light to the floating glasses, Keesha discovers that the light gets even brighter and clearer than ever when shone through Arnold's glasses. She then learns that real things get brighter when there is more light on them and finally comes to the conclusion that it is a trick. When the big footlight burns out, Ms. Frizzle replaces the bulb with a spare bulb.
Back down the basement, Tim and D.A. come across a mysterious figure coming their way, only to learn that it was really their reflection through a mirror. Liz finds a way out and D.A. and Tim follow her. Arnold's ghost is seen once again over the stage and Keesha surmises that Arnold is lit up because there is a source of light up where he is at. She goes up the catwalk using the bulb and finally spots Arnold on top, as well as Janet.
Janet turns on the light and coerces Arnold to hop on one foot. Keesha then discovers that Janet has used the light to shine on Arnold, bounce off of him, and off the glass to show his reflection where the class has been watching him from. Keesha runs to the class to get them to leave. Once the coast is clear, Arnold and Janet attempt to leave the theatre, only to notice that the light has turned out (unplugged by Liz) and the two come across what appears to be a ghost hovering above them. The "ghost" chides Janet for not telling the truth and Janet dismisses this as a trick, only to discover that Arnold is missing (Carlos grabs Arnold). When the "ghost" tells Janet that she is next, Janet runs out of the theatre in fear and encounters the rest of the class, who tell her that they had tricked her to give her a taste of her own medicine. The class also adds that Janet has helped then learn how light works and Tim tells her, "With you around, there's never a dull moment". As the class hop onto the bus, Ms. Frizzle also adds, "It isn't how bright you are that makes you shine, but if you know about light, you can be pretty flashy" right before entering the bus and driving away.
- The relatives Ms. Frizzle mentioned are references to the light bulb inventor, Thomas Edison.
- This is the first time the bus is a limo the second time is in "Meets Molly Cule".
- Janet's trick is based on Pepper's Ghost Effect.
- Gil Filar (the brother of Phoebe's voiceover Maia Filar) is listed on the end credits.