The episode begins with Principal Brown breaking the news about Darwin passing the aptitude test with perfect scores. Since this had never happened before, Brown informs the Wattersons that Darwin has been sent to a government institute for geniuses to have his brain experimented on. The entire family is clearly very upset about this, especially Anais, who claims that the whole operation seems to be a form of quarantine. Brown is intrigued by her insight and wonders if there is another genius in the room, which scares Anais into acting like a fool. Nicole is outraged at this and questions Brown about the ethics of taking her son away from her family, but Brown claims that Darwin is only registered as a "pet fish." and bluntly states that they will never see him again.
Gumball vows to be accepted into the institute as well, which causes everyone else in the room to laugh mockingly. Gumball leaves Principal Brown's office and goes to the School Library to try and study. Meanwhile, Richard and Nicole are outside of the school crying over Darwin, when Rocky comes up to them, carrying a suitcase. They ask what the suitcase is for and Rocky explains that he is having rent problems and doesn't want to stay with his parents. He asks Nicole and Richard if he can stay at their house for a while, which they allow, but on one condition. Back at the library, Gumball runs into Colin and Felix, who inspire him to inflate his head. After accidentally spitting all over them, he meets Bobert who is surfing the internet. He encourages Gumball to try using "the largest source of information in the world", which Gumball attempts but is unable to open up the browser without Bobert's assistance. After he finally clicks the icon, the sheer magnitude and size of the internet causes his memory to overload; meaning he had to be rebooted by Bobert.
Still trying to make himself smart, Gumball looks around the library and sees Teri, Leslie, and two books, reading books. Gumball finally realizes what he has been needing to do this whole time, watch a book. He finds a book, and sits in between Carmen and Carrie, who are both studiously reading. Gumball attempts to watch his book but needs to ask Carmen for help. She is annoyed by him not knowing that he is supposed to read books, and leaves after explaining this.
Meanwhile, at the house, Rocky is dressed up with fins, green pants and shoes (like Darwin), and Nicole and Richard attend to his every whim. As Rocky wonders why he is wearing the clothes they gave him, Nicole creepily tells him to call them mom and dad.
As Gumball struggles to read, Gumball's Brain literally decides that it has had enough and leaves through his ear. Gumball pleads his brain not to go, as he cannot possibly pass the test without it. His brain tells him that it is stupid, after which Gumball decides to train him. This kicks off a training montage with Gumball's brain training itself physically until it becomes strong. Gumball and his brain confronts Brown to take the test, but the brain knocks out Principal Brown with a lamp. Later, at the house, when all hope seems lost, a guilt-stricken Anais reveals that she filled out Darwin's aptitude test. Some Clipboard Men come to return Darwin after they found out Darwin was not the one who had filled out the aptitude test and demand they give them the real genius. To protect Anais, Gumball's brain says that Rocky filled out the test, and they take him away. At the very end of the episode, Rocky is seen being begged to solve an equation, but refuses to do so until he gets everything he wants.
Darwin is rarely seen in this episode, and only has one line of dialogue, despite the plot being about him.
A "Gluteus Maximus" is a muscle that makes up the shape and appearance of the posterior, which means Gumball was called a butt.
In this episode, the other Wattersons don't know that Anais is a genius, yet in "The Goons," they all seem to be fully aware of this. The only logical explanation is that "The Genius" chronologically took place before "The Goons."
During the training montage, Gumball shows pictures of famous scientists for Gumball's brain to break. One of these is a picture of Charles Darwin, who is Darwin's namesake. The other two are Albert Einstein and Stephen Hawking.
After Gumball's brain crashes, the Macintosh SE/30 startup sound is played.
The computer scene is a parody of the start of the Internet video "asdfmovie4."
Towards the end of the episode, when Gumball's brain tries to convince the Clipboard Men that Rocky is the genius, Gumball tells them his brain is "insane in the membrane", a reference to Cypress Hill's 1993 hit "Insane in the Brain."
When Anais tells the family that it was her who filled out Darwin's aptitude test, Gumball's whiskers vanish.
The speaker tells Darwin to write the answer with a dry erase board marker when the board clearly had chalk.
In the episode "The Gi," Gumball was seen using the Internet, but in this episode, he does not know what it is.
Gumball's Brain: That's it. I'm outta here. [Deploys a ladder out of Gumball's ear] I've had enough. I'm off to watch TV.
Gumball: Hey. Where do you think you're going?
Gumball's Brain: I didn't sign up for this. I quit.
Gumball: You can't quit. There's no way I'm gonna pass a test without a brain. Please. I need you.
Gumball's Brain: We'll never pass. I'm stupid.
Gumball: Then -- then, I'm going to make you smart, like Darwin!
[Inside the government facility]
Clipboard Man: Uh, sir? You appear to have a bit... ink on your face?
[Darwin turns around to show his face, covered in ink]
The Watterson's house
Nicole: Are you sure there's nothing else you want, honey?
Richard: Ask for anything.
Rocky: Well, uh, can I have two cans of soda?
Nicole: Quick, Richard -- the fridge!
[Richard quickly runs to the kitchen]
Rocky: Oh, and some jellybeans. But only the yellow ones!
[Rocky questions Nicole while he wears green underwear and shoes]
Rocky: Uh, are you sure there's nothing else to wear, Mrs. Watterson?
Nicole: Please honey -- You can call us "Mom" and "Dad."
[Scene cuts to the School Library. Gumball's Brain can be heard screaming]
Gumball: Read it!
Gumball's Brain: I can't! [Crying]
Gumball: Read it!
Gumball's Brain: It's too difficult! Don't make me!
Gumball: Aren't you tired of being so useless? Years and years of insults and abuse! Remember...
[Zooms in to Gumball's Brain. Visions of Miss Simian, Banana Joe and Principal Brown appear and insult Gumball's Brain]
Lucy Simian: Another "F" for you, Pea Brain!
Banana Joe: [Laughs] Doofus!
Nigel Brown: Loser!
[The three of them laugh and disappear]
Gumball's Brain: Okay, I'm ready.
Gumball: Then prove it.
[Gumball's Brain opens a book and performs a chop, but ends up hurting himself]
Gumball: This may take a while.
Gumball's Brain: [Falls]
[They perform a song while Gumball's Brain gets stronger]
Man: I was a feeble minded guy. I'd slip on ice and wonder why. So many obstacles were thrown my way, on a downward slide each and every day. But something popped inside my brain. I got up to fight that fight again. And I knew what to do. I went through the mental pain. You gotta think big, think deep. Pretty soon you'll make that quantum leap. Think big, think smart. Make your brain your finest body part! The greatest minds from yesterday, will be crushed to dust 'cause I'm on my way. (Big, big, big) You gotta think big!
[Gumball and his Brain freeze frame while jumping. Idaho walks by, and wonders why they are doing that, but he shrugs it off]
[Scene cuts inside Principal Brown's office while he's enjoying his coffee, when suddenly Gumball surprises him]
Gumball: I want to take the aptitude test!
Nigel Brown: Hmmph! You don't have the brain of the genius, Watterson.
Gumball: We'll see about that. Come on, brain -- show Principal Brown what you can do.
[Gumball's Brain grabs a desk light and swings it at Principal Brown, knocking him unconscious]
Gumball: What the -- What is wrong with you?! I meant do an equation or something.
Gumball's Brain: Oh. Sorry.
Back in the Watterson's House
[Scene cuts inside Watterson's house with Rocky walking around]
Anais: [Looks at Gumball's brain] I always pictured it a little smaller.
Gumball's Brain: I've been working out.
[Rocky sits with Anais and Gumball]
Rocky: Hey, dudes, want some popcorn? [Shouts to the kitchen] Dad, can I borrow Mom's car tonight?
Richard: Sure, son. Anything you like.
Rocky: Man, my dad is a righteous dude.
[Gumball notices Rocky's strange attire]
Gumball: Mom? What's going on here?
Nicole: Oh. Well, this is your new brother -- Rockwin.
Gumball: You're kidding, right?
Nicole: Come on. Let's just all give it a try. Just for a moment. [Humming]
Gumball: [Shouts] It's not working!
Nicole: [Sighs] You're right. It's not.
Richard: [Interrupts Nicole] Just a minute. [Hums, then stops] No, it's not working.
Gumball: [Gumball starts crying] I miss Darwin so much.
[Everyone starts sighing, except Anais. Then Anais interrupts]
Anais: All right! It was me!
Anais: It was me who filled out Darwin's aptitude test. I found it on the TV guide. I should be the one taken away.
Gumball, Nicole, Richard, and Gumball's Brain: So Darwin's not a genius?
Anais: No. I am.
[Suddenly the doorbell rings. They open the door and see Darwin]
Gumball, Richard, Nicole and Anais: Darwin!
Clipboard Men: We believe this, is yours.
[Darwin steps inside the house]
Gumball: Welcome back, buddy!
Nicole: I missed you so much.
Anais: Don't ever go away again.
Richard: What a conveniently happy ending.
[The door starts to close, but a Clipboard Man prevents the door from closing with his leg]
Clipboard Man: Not so fast.
Richard: Hey. I said it was a happy ending.
Clipboard Man: You still owe us one genius.
Gumball: What do you mean?
Clipboard Man: Well, it's obvious he didn't take that test.
[Darwin gives a stupid look]
Clipboard Man: But someone in this house did, [Rips off the other Clipboard Man's paper, showing a Warrant] and this warrant says that we get to take that person away.
[Everyone gasps again]
Clipboard Man: Who is it?
[They begin to get anxious]
Gumball's Brain: Ahem. I know who it is.
Gumball: [Gasps] Be quiet. Don't listen to him. He's insane in the membrane.
Gumball's Brain: Don't worry. I know what I'm doing.
Gumball: No, you don't. You're stupid. We've established that.
Clipboard Man: Let the brain speak.
[A heartbeat sound can be heard as each person's worried face is shown. Then cuts to Rocky drinking soda and creating the heartbeat-like sound]
Rocky: [Burps] Sorry.
Gumball's Brain: The person who took the test was... H-h-h-h-h-h-h-h-h-h-h-h-h-h-h-- him! [Points at Rocky]
Gumball's Brain: [Winks]
Rocky: Oh. Yeah, I took that test.
Clipboard Man: Then get your suitcase. You're coming to the research center.
Rocky: What, you mean like, for free?
Clipboard Man: Well of course.
Rocky: Eh, definitely beats my parents' place.
[Scene cuts inside the car with Rocky in it]
Rocky: Oh, and I'm gonna need a hot tub, too -- 'cause I do most of my thinking in the bath.
[The car leaves]
Gumball: See ya, Rocky.
Nicole: Bye, Rocky.
Gumball: That was really smart, Brain. Darwin's back home.
Gumball's Brain: Can I come home too?
Gumball: Are you kidding me? Get in there, little dude.