The episode begins with a virus army on Gumball's fur. The leader of the army rallies the troops, giving an inspirational speech about how they will use Gumball's body as a stepping stone to their ultimate goal of infecting everyone in the world. As they charge towards Gumball's nostrils, the ground beneath them shakes. The cause of this sudden movement is Teri attempting to force Gumball to wash his hands in the water fountain. After learning why he refuses to wash his hands (as well as his disturbing method of showering without his hand getting wet), she is able to overpower him and finally clean his hands. The screams of the virus army as they are washed down the drain can be heard, but Gumball dismisses it as nothing. After the three of them leave, it is revealed that the leader of the virus army has survived, and he plots vengeance for his fallen comrades.
Later that day, the class does computer work at the library, though most of them use the time to play Space Invaders. Gumball and Darwin, unaware that Teri is right next to them, begin to mock her obsession with cleanliness. She announces her presence, angrily, causing the two of them to apologize. Then she uses Gumball's computer to show them a picture of a finger that has not been disinfected after a paper cut. Gumball and Darwin reel back in horror at the disgusting picture. Darwin, suddenly afraid of germs, grabs some of Teri's disinfectant substance and rubs it all over his body. Gumball, on the other hand, remains nonchalant about germs, mocking their fear of it and dismissing germs as a part of life. Teri counters with the fact that keyboards generally have more germs than a toilet seat. Gumball sighs and begins licking the keyboard in a show of defiance. Unfortunately, the vindictive virus was on the keyboard, waiting for an opportunity to infect Gumball, and his exposed tongue was just what he was looking for. He gets sidetracked by the various bacteria that were also on the keyboard. Unwilling to let them infect Gumball instead of him, he fights them all off. Just as he finishes the last one, Gumball finishes licking the keyboard, causing him to scream in exasperation.
The scene cuts to the science room, where Gumball is using a microscope to check Darwin's butt for hair. He does not find any, concluding that Darwin will never grow a beard, which saddens him. Teri again chimes in, telling them that an average butt has more germs than a toilet seat. Gumball explains that he is not scared because he never gets sick. He goes on to explain that he can make his body do whatever he tells it to. He demonstrates this, rather disturbingly, by performing several movements considered biologically impossible for a vertebrate. After convincing Teri of his fascinating ability, he collapses in pain and is brought to the nurse.
At the nurse's office, the School Nurse explains that Gumball's organs are scattered throughout his body, but he is otherwise healthy. Teri is visibly and audibly flabbergasted at the nurse's outrageous diagnosis. The nurse believes she is talking about the treatment she gave Gumball, but Teri is actually talking about herself. The nurse, annoyed with Teri's frequent visits, recounts all the times she panicked when nothing was wrong with her. Teri, having no rebuttal, simply sighs in defeat.
Back at the science lab, Gumball and Darwin continue chiding Teri, much to her annoyance. She angrily rips a hair off of Gumball, innocently explaining that she just wanted a hair sample. Upon examining said hair sample through a microscope, she discovers a deadly, malevolent virus. Gumball guesses her thoughts, and he and Darwin give her sarcastic looks. Teri pleads for them to at least look at her discovery, and when they refuse, she pretends to cry. Gumball, falling for her sad eyes, obliges her. He looks through the microscope and, to his surprise, finds out she was telling the truth. Darwin looks at it as well, and witnesses it evolving to grow wings. He relays his sightings to the group, causing Teri to panic and put on a facemask. Teri urges them to move to a sterilized environment.
The "sterilized environment" ended up being the Wattersonhousehold. Gumball gets on his laptop and looks up a cure to the virus, but Teri thinks of giving up, explaining that viruses are able to evolve to adapt to any situation, thus rendering any attempt to stop it useless. Darwin, remembering the old phrase "fighting fire with fire," begins to attempt mutating himself, with disappointing results. Suddenly, Gumball gets an email from a website called "FreeOnlineMedicationWithoutPrescription." Thinking he has found the answer to this problem, he excitedly opens it. Unfortunately, it turns out to be the virus. It takes over the computer and starts taking over all of the house's electronics. He uses them in an attempt to kill the trio.
Gumball, Darwin and Teri escape into the backyard, and narrowly dodge a saw thrown at them. Chased to the streets by a lawnmower, the trio catch their breath and assume they are safe, being away from all the appliances. However, the lawnmower touches a car, and the Virus mutates again and takes control of multiple cars.
The trio is chased into an alley, and are backed up against a wall. Gumball challenges the Virus, calling him out on his cowardice for attacking three kids with five cars. The Virus is offended, and deactivates the cars. The Virus approaches the trio, giving a long speech about Gumball's demise. While the Virus taunts, Gumball merely steps on him, ending the episode.
In reality, bacteria are larger than viruses, but when Gumball licks the keyboard, the bacteria shown are smaller than the Virus.
This episode aired in Spain before an airdate was even announced in the US and UK.
This episode aired in the UK before the US.
It was revealed in this episode that Teri's mother is a doctor.
The Virus' threats to rid the world of all living beings may be a reference to the fact that viruses are not classified as living things.
This episode was the most viewed in Season 2 with 2.570 million viewers, surpassing even the season premiere. It is also the most viewed episode of the show as a whole so far. 
Based on what the School Nurse said about Teri's false alarm sicknesses, this episode takes place on a Thursday.
The wrestling tape seen in "The Prank" and mentioned in "The Club" can be seen on top the TV.
This is the second time we see Darwin's butt. (The third time if you count the trailer.)
This is the second episode in which a character dies on-screen. In this case, it is the Virus and his army. The first time was in "The Picnic."
The game all the kids were playing on the library computers was Space Invaders.
"Mumu," the GPS seen in one of the cars, is a reference to TomTom, a Dutch GPS manufacturer.
At the beginning of the episode which shows the viruses on Gumball, Gumball's fur looks similar to Grover's fur from Sesame Street.
The Virus' statement "I hope your body is ready" is a reference to a meme, and a quote from Reggie Fils-Aime.
The Blue Screen on the laptop has the same text as the Windows 98 and 95 BSOD, which would explain how the Virus easily took it over, seeing as both versions are unsupported, and thus, don't get vital security updates.
When Carmen stops playing Space Invaders to pretend to do homework, her computer screen turns pitch black, unlike the other kids' computers.
When the Virus transfers from the laptop into the electrical system, Teri is shown being as short as Darwin.
[The episode starts with tons of virus organisms on Gumball's fur, then one of them stands on a hill-like lump of fur]
Virus: Brothers, we've mutated many times over for this moment, but now we are ready. Today, we take this body; tomorrow, the REST OF THE WORLD!
[The virus army starts cheering and raising their fists]
Virus: None will be safe from our infection! Our glory will be greater than the pox, the plague and bad flu combined!
[One virus grunts as he pounds his chest]
Virus: [Raises his fist] Follow me to the nostril!
Virus Army: Hoorah!
[The army follows the leader as he charges, but they all stop when the ground starts to shake]
[Scene changes to the school corridor where Teri is forcing Gumball to wash his hand; Darwin stands nearby, watching them]
Gumball: [Struggling] Get off! Why don't you clean your own hand, you clean freak!?
Teri: Wash it now, you disgusting biohazard!
Gumball: [To Darwin] Man, for a paper girl she's surprisingly strong.
Darwin: I think it's more like you're surprisingly weak.
Gumball: [To Teri] I don't want to wash it! [continues to resist Teri's efforts]
Teri: What is your problem?!
Darwin: [Sighs] He got a high five from Penny three months ago and refused to wash it since.
Teri: [Shocked] Don't tell me you haven't showered in ninety days.
Gumball: Of course I've showered, I'm not an art student. I just wrap my hand in swimming trunks to keep it dry.
Darwin: Ask him how often he washes those.
Gumball: You don't wash swimming trunks, they clean themselves when you swim. [Puts his hands on his chin] Right?
[Teri backs away from Gumball in disgust]
Teri: Ewwww! When Penny hears that, she'll be so horrified that her antlers will turn white.
Gumball: Please don't tell her!
[Gumball stares at his hand, pondering]
Gumball: What if I just cut it off and keep it in a memory box?
Teri: [Grabs Gumball's hand and drags it into the fountain] Just wash it!
Gumball: [While his hand gets washed] Noooooooooo!
[High-pitched "Nooo" sounds are heard from Gumball's hand, followed by drowning sounds]
Darwin: Did you hear that?
Darwin: Kinda sounded like a choir of gnomes going down a waterslide.
Gumball: What, like- [Imitates the sounds almost perfectly]
Darwin: Yeah... exactly.
Gumball: Nah, didn't hear it.
[Camera zooms into the sink where the Virus Leader, the only survivor, is lying flat on his face]
Virus: [Wakes up] I will find you, and when I do, I swear on my fallen comrades, I will infect you, and I will destroy you, and then I will take over your family, your friends and I won't stop until nothing is left alive on the surface of the Earth! DO YOU HEAR ME?!
[Camera zooms out, showing an empty school corridor]
Virus: [High-pitched voice] DO YOU HEAR ME?!
The School Library
[The school bell rings and the scene changes to the school library where Gumball and several students are playing Space Invaders. When the librarian walks past, all of the students pretend to do homework]
Gumball: [Turns flat and makes a bad impression of Teri] You may want to clean up the alien slime on your laser gun. You could get sick from that!
Darwin: [Turns flat and imitates Teri as well] I always carry my intergalactic antibacterial gel in case I need to interfere with people's lives.
[Both of them snicker]
Teri: [Appears out of nowhere] I'm right here, you know!
[Gumball and Darwin scream]
Gumball and Darwin: Sorry.
[Teri closes the Space Invader game and uses the internet]
Gumball: Hey, I just picked up the proton bazooka!
Teri: If you think germs are so funny, then maybe you should look at THIS!
[Teri enters a website using the keyboard]
Gumball: OH MY GOSH, what is that?
Teri: That's my mom. This is her website. She's a doctor.
Gumball and Darwin: Oh.
[Teri goes to another page]
Gumball: OH MY GOSH! WHAT IS THAT!?
Teri: That is what happens to a finger if you don't disinfect a cut.
Darwin: It looks like a purple foot covered in mayo!
[Teri squirts some sanitizing gel onto her hand]
Teri: And that only came from a paper cut!
Darwin: GIVE ME THAT! [grabs Teri's bottle of sanitizer and rubs it all over himself, growing multiple arms in the process]
Darwin: [to Teri] Can you do my back?
Gumball: [Makes a impression of Teri] Oh no, evil germs are out to get us! [Changes back to his normal voice] The germs are fine, man! They're part of life, that's Mother Nature trying to make you stronger!
Teri: Oh really? You do know that the keyboard you just used has more germs on it than a toilet seat?
[Gumball sighs and licks the keyboard then the camera zooms into the keyboard where the Virus can be seen]
Virus: YES! My chance for revenge! [Bacteria start appearing behind him] Huh? Stay back, bacteria, he's mine!
Green Bacteria Minion: Come on, virus, there's plenty to share!
[Bacteria starts charging towards Gumball's tongue]
Virus: I SAID GET BACK!
Bacteria Minion: [While the Virus hits them] Right at the flagella! Right at the ribosomes! [The Virus grabs one of the bacteria and uses it as a weapon] Dude, not the cytoplasm! [The Virus smacks another bacteria] It hurts me too you know! [The Virus throws the bacteria towards a giant blue bacteria] Ahhhhh!
[One of the bacteria gets past the virus and reaches the tongue]
Virus: Hey! I said get back!
[The Virus catches the bacteria and shoots him like a torpedo towards the other bacteria, causing a big blue explosion]
Virus: Hahhaha! [Turns around] Huh? [Sees Gumball's tongue and it's leaving in the keyboard] NOOOOOOOOOOOOOOOOOO!
To the infirmary
Gumball: Nearly there... just focusing... and... yep. You're right. There's definitely no hair on your butt. [places microscope back] I don't think you'll ever grow a beard, man.
Teri: You do know there are more germs on a pair of buttocks than the toilet seat, right?
Gumball: [scoffs] I don't care. I'm one of those people who never get sick anyway.
Teri: What, a liar?
Gumball: No, I just tell my body not to get sick.
Teri: [sarcastically] Oh really? And how do you do that?
Gumball: The power of the mind over the flesh. I can control any part of my body. Watch.
[He moves his ears all the way down to his chin. He then rotates his arms and torso as his legs move straight up and down.]
Gumball: You believe me now?
Teri: Uh, yeah, sure.
Gumball: Good, 'cause now you're gonna have to take me to the infirmary.
[Scene changes to the infirmary. Gumball is on the bed, stuck in his pose.]
Joan: [examining Gumball] Well, your heart's in your stomach and you'll be breathing out of your arm for a while but apart from that you're hunky-dory. [Fixes Gumball's arms]
[Gumball and Darwin hug, sighing with relief.]
Teri: What? Where did you get your diploma? The World College of Ducks? 'Cause you're a certified quack! You haven't run a blood test, taken a temperature or even an x-ray!
Joan: He's fine, he just needs to walk it off.
Teri: I'm talking about me! [points at Gumball and Darwin] I've been in contact with these germ-bags all day! [weak voice] I can feel myself getting ill...
Joan: Hmm, like Monday, when you thought the foam in your mouth was rabies only to discover it was toothpaste? Or Tuesday, when you thought you broke your leg even though you don't have any bones? Or yesterday, when you thought you'd gone deaf because nobody had spoken to you for five minutes?!
[Teri inhales angrily, and sighs as she droops her head]
[The scene changes to the school lab. Gumball, Darwin and Teri are using microscopes.]
Gumball: [To Teri] You know, I think I've actually found a disease you suffer from. Attention-seeking-itis. [gasps] Dr. Darwin, is there a cure?
Darwin: [deep voice, pretending to be a doctor] Yes, getting a life.
[Gumball and Darwin snicker, Teri plucks a strand of hair from Gumball]
Teri: I just needed a hair sample. [looks at the strand through the microscope, then gasps]
Gumball: [sighs] Lemme guess, you found a deadly virus previously unknown to science, and it's coming after us.
Teri: Yes, exactly.
Gumball: [sarcastically] Oh no! What should we do, Dr. Darwin?
Darwin: [pretends to be a doctor again] I recommend a high-dose treatment of sarcastic looks.
[Gumball and Darwin fold their arms and look sarcastically at Teri]
Teri: Could you at least look at it?
[The boys do not respond. Teri sniffs, and draws a tear on her cheek]
Gumball: [sighs] Alright, whatever. [looks through microscope] What the pox? [sees the Virus, who seems to be insulting Gumball] Dude, she's right! There's a virus. And he's making rude gestures at me with those little tentacles!
[Darwin looks through the microscope as well. He sees the virus grow wings.]
Darwin: What does it mean when a virus grows wings?
Teri: [panicks] Let me look. [looks through microscope]
[The Virus starts flying towards them.]
Teri: [gasps] It's mutated and gone airborne.
[Teri grabs a pencil, erases her mouth and draws a surgical mask in its place.]
Darwin: Give me that! [grabs pencil and also draws a mask on his face]
[Teri tries to speak, but is muffled.]
Gumball: Hold on. [draws Teri a tiny mouth]
Teri: [small voice] We need to hide in a sterilized environment. [erases mouth again]
Finding the cure
[Scene changes to the Watterson living room. The kids are on the couch. Each are wearing protective gear: Darwin is in his fishbowl; Gumball has a plastic inflatable ball over his head; Teri is folded inside a clear plastic paper sleeve. Gumball is browsing on his laptop.]
Gumball: Which virus do you think it is?
Darwin: Let's read the symptoms.
Teri: [sighs] What's the point? We'll never know which virus it is if it's always mutating. [whispers] They're the worst, they always find a way to get you.
Darwin: Then we need to fight fire with fire! [concentrates]
Gumball: What are you doing?
Darwin: Trying... to... mutate! [cracks the fishbowl] Ah!
[The laptop beeps]
Gumball: [gasps] An email from free online medication without prescription!
[The laptop starts growling and moving on its own.]
Gumball: Uhh, did you see that?
[Darwin and Teri have leaped out of their protective gear and the couch. The laptop starts attacking Gumball.]
Gumball: Can I get a little help over here?!
Darwin: Try to turn it off and on.
[The laptop bites at Gumball, and tears off the ball on his head. It spits it out and jumps at Gumball again]
Gumball: Ahh! Darwin! Unplug it! [runs away]
[The laptop growls at Darwin, and starts barreling towards him. Darwin screams as the laptop nears, but then Teri charges in and douses the laptop using a mug of water. The laptop's screen turns blue, then shuts down.]
Darwin: Ah! I told you PCs were unreliable.
[The Virus' face appears on the TV screen]
Virus: You thought you had escaped me, but you thought wrong. I am a warrior who can never be defeated. I have mutated and now I'm gonna take-
[Gumball mutes the TV]
Gumball: Let's get out of here while he's still talking [his hand goes towards the doorknob]
[A compact disk flies at the door, embedding itself into the wood. The Virus starts launching CDs from the stereo]
Gumball: Huh? Get down! It's a multi-changer! [They take cover behind the sofa]
Darwin: How did he get into the stereo!?
Teri: He's mutated and infected the entire electrical system!
[Several appliances start floating and moving towards the sofa.]
Gumball: Every electrical device in this house is coming after us, it'll be safer if- [an electric razor attacks Gumball] Ahh! [sits up; his eyebrows are missing] Aww man, not the eyebrows!
Teri: How exactly do you feel about that? Angry? Surprised? Upset? I can't tell.
[Gumball grows his eyebrows back]
Darwin: On my command! Three! Two! One!
[The music stutters, and the disk slot on the stereo opens]
[The kids run into the kitchen]
Teri: How did you know that would happen?
Darwin: My mix-tape is all scratched up. It always jams. [screams; the waffle iron has clamped onto his foot] The waffle iron!
Gumball: Oh my gosh! Your leg! Is it burning?
Darwin: [calmly] Nah, I overreacted. It's warming up really slowly. [removes the iron from his foot]
[The toaster starts shooting bread at them, so they take cover behind the fridge door]
Gumball: But what do you want from us?
Virus: [using the boombox] I want my vengeance! You washed away my army, and now you shall PAY!
Gumball: [to Teri] I told you I shouldn't have washed my hands. [to the Virus] Well you're not gonna destroy us with pastry! [gets a mouthful of pastry in his mouth]
Virus: The pastries were just a decoy, my friend.
[The microwave crackles and shoots rays out, burning the Robinsons' roast turkey next door. Gumball, Darwin, and Teri run out to the backyard]
Gumball: Shh, what's that sound?
[Scene changes to the shed. A rotary saw blade flies out the door. Gumball and Darwin duck. They look down, and Gumball gasps. Teri appears to be decapitated.]
Gumball: Teri... are... you okay?
[Teri does not respond]
Gumball: She's not answering.
Darwin: I think it's for the best. 'Cause if she tried to talk, she'd sound like [makes gurgling sounds].
Gumball: [sobs and kneels] I'm so sorry, Teri. I shouldn't have made fun of you.
Darwin: [sobs and kneels as well] At least, she doesn't need to worry about germs anymore.
[Teri suddenly sits up, head intact]
Teri: Watch out! [Gumball and Darwin scream in surprise] No, behind you! [points]
[The lawnmower bursts out of the shed. Gumball, Darwin, and Teri dodge it. They jump over the fence, and the lawnmower plows right into the fence]
Gumball: [panting] That was close. We should be safe out here, there's no electrical stuff.
[The lawnmower bumps into a parked car. A wave of electricity washes over the car and it starts. The virus' face appears on the car's sattnav.]
Sattnav: System online. [The Virus laughs evilly]
Gumball: Oh man, he's mutated again!
[Several cars nearby also start, then they barrel towards the kids, who then run away.]
Gumball: I've got an idea! [flips a stop sign towards the cars]
[The cars completely ignore the sign, plowing into it as they continue the chase]
Gumball: I thought he'd at least slow down at the stop sign.
[The cars surround them]
Teri: Quick! Down the alley!
[The cars follow them down the alley, and corner them. Gumball steps forward and berates the Virus]
Gumball: Hey, Virus!? Where's the honor in this!? Five cars against three kids? I thought you were a warrior, not a coward!
Virus: Who are you calling a coward? I don't need an army to take you down!
Gumball: Then come out and fight me like a man!
Virus: You're on!
[The cars turn off; one of the cars get the hood flipped open, revealing the Virus]
Virus: I hope your body is ready, because I'm gonna turn it into a cesspit of pain. Not just regular pain, it will be a seven-course banquet of pain. There will be a starter of suffering, a fish course of torment, and excruciating dessert! And just when you think you're full, you'll be served... a coffee and biscotti of misery!
[Gumball simply steps on the Virus, producing a "SQUISH" sound and subsequently ending the episode.]