The episode begins with Gumball announcing to Darwin his latest creation; "the gross jar," a jar filled with many gross things such as bird feces and regurgitated spoiled milk, and proclaiming it to be the best thing ever. Darwin says Gumball said that his Tap Dancing Dolphin impression was the best thing ever, but Gumball says that the jar blows that out of the water. While they discuss what they are going to do with the jar Richard mistakes it for his coffee cup, which he grabs and throws it into the microwave. Gumball and Darwin agree to nuke it, to their inconvenience of the jar already being heated up in the microwave.
Suddenly, an "eye" forms in the muck of the jar. Gumball and Darwin watch in fear as the timer goes off. They observe the jar and find a little monster face inside the muck. Gumball finds it first and exclaims they have a baby. Darwin screams he does not want to be a father and proposes to trash it. Gumball tells him to keep quiet to not hurt his feelings, but Darwin tries to skip out. Gumball promptly tells him to stay put and help out his new "son."
Gumball then tries to ease him out the jar, as Darwin makes cute remarks towards the baby. However, the baby jumps out and sucks on Darwin's eye. Darwin screams and tells him to get off, in which Gumball replies it is merely something babies do. Gumball tries to pull him off, but he starts sucking on his neck. Darwin then claims it is hungry, so they try to find something to feed it with. Anais walks to the kitchen to find the monster baby sitting in her stool. She demands to know what it is, in which Gumball and Darwin explain it is their child. Anais continues to insult it until Gumball tells her to stop insulting Kenneth, which is revealed to be what they named the baby.
The boys then leave to get some pigeon traps leaving Anais to go off and babysit for a while. Anais groans and starts examining the monster, only to scream out in horror as it attacks her. Gumball and Darwin come back to find Anais gone, and Darwin exclaims that Kenneth grew. The doorbell rings in which Kenneth runs off and attacks the delivery man at the porch. Gumball and Darwin come out and find him eating away at the trash cans. Gumball then claims they need "parental advice."
They go to the backyard where their father is getting a suntan and ask for help. Richard says that they need to lay down the law and explain their superior position. While he explains that you should not give your dog or child attention for anything wrong, Kenneth continuously swallows his arm. Gumball and Darwin point out that Kenneth is slowly eating him, but Richard claims it is fine until he is eaten. The boys scream and run away, realizing Kenneth has vastly outgrown them and infer that he ate Anais and the delivery man.
Later that night, Nicole comes home to find the boys hidden in the front room. Gumball unintelligibly explains that they have made a monster that ate everyone. Nicole does not understand in which Darwin explains also in a quick unintelligible way that they made a monster and they need to call the army. Nicole still does not understand so she reassures them it is a raccoon and goes out in the backyard to look for Richard. Nicole then wanders around the foggy backyard cautiously until she is attacked and eaten by Kenneth.
Gumball and Darwin then try to stop him but the monster catches them off guard. Kenneth leaps at them, but they run off as he gets caught in the fence. Gumball and Darwin then try to beat him up with gardening tools before realizing the entire family is inside. Richard then reassures them that it is not so bad in here, but that they should hurry up and get them out. Darwin then proposes to use the gardening hose as a cable so that he can jump in Kenneth's mouth and grab everyone, then Gumball can pull him out. Gumball objects, but it is too late. Darwin gets swallowed into the monster.
Gumball then tells the anxious Darwin that the plan can not work because the monster has the rope in-between his teeth. Darwin then tells him to think of something, but Gumball admits he has no idea what to do. Gumball then gets thrown back by Kenneth's roar and accidentally turns on the water to the hose. The monster gets filled up to breaking point and explodes, setting everyone free. They all rejoice, and Gumball lies that he did it on purpose. Then they find little Kenneth now vastly smaller on the lawn. Gumball then talks cutely towards it. Richard then tries to destroy it, but Gumball assures him that Kenneth was merely misguided and that he is a nice creature. With a touching speech, he convinces the family to give Kenneth a second chance. Cut to the future, where Kenneth, instead of being gentle, turns out to be an even bigger monster than before, destroying the town. Gumball and Darwin reflect on their decision, now believing that they should have just destroyed him when he was little.
[The episode begins with a shot of the house as we then see the interior and Gumball holding up his gross jar]
Gumball: Behold, Darwin. The grossest thing ever! I shall name it the gross jar! It will be my legacy to the world! It's the coolest thing ever.
Darwin: But I thought that my tap-dancing dolphin impression was the coolest thing ever.
[Darwin imitates a dolphin, complete with dolphin noises and tap dances to music]
Gumball: Yeah, but this just literally blew you out of the water.
Darwin: [Sad dolphin noise] What's inside?
[Montage of Gumball sneezing and disposing the used tissues in his gross jar, feeding birds and collecting poop, picking lint out of Richard's belly button and Richard drinking out-of-date milk and Gumball holding up the gross jar, winking. We cut back to a rather confused Darwin]
Darwin: O...kay. So what are you going to do with it?
[Richard walks into the kitchen behind the two, looking half asleep and yawning as he mistakes the gross jar for his coffee and puts it in the microwave]
Gumball: Yeah, well, that's the problem. I don't really know. It needs a final touch to make it a true masterpiece.
[Richard turns on the microwave]
Gumball and Darwin: [Both gasp simultaneously] Nuke it!
Richard: Could you tell me when my coffee's ready? I'll be in the garden.
Darwin: What's going on?
[Both look directly at the gross jar which mysteriously creates an eyeball. Gumball and Darwin scream]
Gumball: It's looking at me!
Darwin: Dude, where did you find an eyeball?
Gumball: I-I didn't. It must be the atomic power of the microwave.
[The microwave dings, and smoke appears]
Darwin: It looks like it's alive.
[Gumball opens the microwave door, then takes out the gross jar. Eyes and a mouth are created]
Darwin: Did you hear that? It called you "Mom."
Gumball: Hmm. Then I guess that makes you its dad.
Darwin: Its dad?! Aah! What are we gonna do?! I don't want to be a baby father! Let's ditch it!
Gumball: Shh! Don't say stuff like that in front of him! I mean, come on. He's kind of cute. Hello, little guy.
Gumball: Don't you worry about a thing. Me and your father will take care of everything.
[Darwin sneaks away and Gumball sees him]
Gumball: [Angrily] Darwin! Where do you think you're going?!
Darwin: [Nervous] Uh… to buy some stuff? At the shop?
Gumball: What are you doing?! He's your son.
[Darwin sees Kenneth's cute looking body, then he cries]
Darwin: [Cries] I'm sorry, little guy. From now on, I'll always be there for you.
Gumball: [Gasps] Darwin, I think he's ready for his first steps.
Darwin: Wait! [Goes off-screen, and returns carrying a camera] Go ahead. Come on, don't be shy. Come to Daddy. Aww! He's kind of got my eyes. Don't you think? [Kenneth jumps out and starts eating his eye] Aah! He's got my top lip, too!
Gumball: Dude, it's what babies do. He's just suckling.
Darwin: It's not suckling! It's eating!
Gumball: Okay, relax. He's just playing. He'll come off on his own.
Darwin: [Calms down] Okay. Okay. Okay. Aah! His teeth are sinking in!
Gumball: Okay, that's enough! Bad baby! Stop mauling your father and get back in your jar this insta—
[Kenneth tackles Gumball and bites his neck]
Gumball: Aah! Aah! He's got my neck!
Darwin: I know what it is. He must be hungry.
[Kenneth is in a high chair. He breaks a plate, snarling hungrily and excitedly]
Darwin: Okay, so it doesn't like fruits, vegetables, or cereal. But it does like pigeons, rats, raccoons, seagulls, and the mailman's butt.
Anais: What was all that noise? What are you two up— Aah! What is that thing?!
Gumball: It's our baby.
Anais: What are you talking about? Where did you find it?
Darwin: It came out of the microwave.
Anais: Are you sure it didn't come out of the toilet? It's disgusting.
Gumball: They always look a bit funny when they're just born.
Darwin: He's actually very advanced for his age.
Gumball: You should have seen him catch that seagull.
Anais: What?! You let that monster out?
Gumball: [Through his teeth] Look, I was trying to be nice here, but you better stop insulting our child or I don't know what I'll do.
Anais: It's not a child! And what is it doing in my high chair?
Gumball: Don't listen to her, Kenneth. She's just jealous.
Anais: [Confused] You called it "Kenneth"?
Gumball: Baby needs a name. Look, like it or not, you're Kenneth's aunt. Now, we're gonna buy more pigeon traps. You babysit.
Anais: Are you crazy? What do you think you're—
[Gumball and Darwin leave]
Anais: I guess you're kind of ugly cute.
[Scene changes to Kenneth's point of view]
Anais: What kind of animal are you? Wow. Those are pretty pointy teeth.
[Kenneth gets out of the high chair]
Anais: What the— Aah!
[He jumps at Anais and she screams in fear. Later...]
Gumball: Kenneth, we're home!
[Gumball drops his pigeon traps and he sees the messy room. Kenneth has gained weight. Anais is nowhere to be seen]
Gumball: Ah! What a mess.
Darwin: Where's Anais?
Gumball: Eh, I knew she'd bail.
Darwin: Gumball, has Kenneth grown?
Gumball: Grown into a trouble maker. This place is a mess! Naughty Kenneth.
[The doorbell rings]
Gary: [Off-screen] Parcel for the Wattersons!
[Kenneth jumps out the high chair and runs to the front door]
Gary: [Off-screen] Hi. Waah! Whoa!
[Gumball and Darwin burst out the door while Kenneth slurps up the mailman]
Darwin: [Notices Kenneth is even bigger] Did Kenneth just eat the mailman?
Gumball: Uh, no, no, no. That's not possible. Not my Kenneth.
Darwin: Well, where is he, then?
Gumball: What do I know, mailing? I'm more worried about Kenneth. Does it look to you like he's gaining weight?
[Kenneth is seen eating garbage]
Darwin: I'm more worried about his attitude. This boy needs discipline.
Gumball: [Sighs] I think we need parental advice.
[Richard relaxes in the backyard. He tans himself, with cucumber slices covering his eyes]
Gumball: So, um, we're doing this school project.
Gumball: And, uh, we've got to look after this, uh, gross dog thing.
Richard: I'm with you.
Gumball: And we need your help disciplining it.
Richard: [Gets up] Okay. It's pretty simple, kind of like children, actually. The first thing you have to do is to let it know you're the pack leader. So you look them in the eyes and tell them firmly you're the boss. [Points at Kenneth] Now, you've been a naughty doggy!
[Kenneth consumes Richard's finger]
Gumball: Dad, he's got your finger.
Richard: Well, that's to be expected, son. The best thing to do is to remain calm and reassert your authority.
[Kenneth consumes Richard's arm]
Gumball: Yeah, but it seems to be eating your arm.
Richard: Ha ha ha. It's just testing its boundaries. The worst you can do is give it attention for negative behavior.
[As Richard talks, he is slowly eaten by Kenneth]
Richard: I have always found that a positive reinforcement approach is the best way to— [Gets eaten completely]
Gumball and Darwin: DAD!
Gumball: Kenneth's eaten Dad!
Darwin: Probably Anais, too!
Gumball: We've got to save them!
[Kenneth finishes eating Richard, and roars at the two]
Gumball: We'll save them later!
[Gumball and Darwin run away, screaming]
The Fight Against Kenneth
[Gumball and Darwin barricade the house. At night, Nicole comes back home]
Nicole: Hey kids. Sorry I'm late, I— [Gets hit by a bucket] Ow! What the—
Gumball: [Talking very fast] Mom, something terrible in the garden became in the microwave and became alive and swallowed the mailman and dad and Anais and wants to eat us and we got here, and—
Nicole: [Confused] What?
Darwin: What Gumball is trying to say is [Panicking] the microwave monster was nice at first, but then it ate everyone! It's horrible and it's in the garden and it's really dangerous! We need to build an army to— [Babbling]
Nicole: Okay, slow down, boys. Where's your father?
[A sound from the backyard causes Gumball and Darwin to gasp and look at Kenneth walking through the window. Then they scream]
Gumball and Darwin: It's turned to a monster, and now it's coming to get us!
Nicole: Oh, for goodness' sake. It's probably just a raccoon. I'll go and check. You stay here. [Walks to the backyard]
Gumball and Darwin: No! Don't go outside!
[Nicole goes outside, wary]
Nicole: Richard? Where are you? What's wrong with the kids? They haven't been this scared since you made them wax your back. Richard, you better not be trying to scare me.
[Nicole steps on a rubber duck, and is startled by it]
Nicole: [Sighs in relief] Oh! Aww. Richard? Richard, stop playing games.
[Kenneth sneaks from behind, and towers over Nicole]
Nicole: Richard? Aaaaaaah!
[Nicole looks up, and screams. Back inside…]
Gumball and Darwin: Mo-o-o-o-o-m!
Darwin: This is all our fault! It's because we're bad parents!
Gumball: Kenneth has grown up to be a troubled child.
Darwin: A troubled child that eats people! We've got to do something!
Gumball: You're right. No video games for a week.
Darwin: [Crosses arms]
Gumball: Uh, grounded for two weeks? Okay. Let's send him to boarding school.
Darwin: Stop being so soft! We have to stop him now!
[Gumball cries. Cuts to the both of them creeping around out in the backyard, carrying tools for weapons. An owl hoots]
Gumball: What was that?
Darwin: It's an owl.
[They continue walking. A twig cracks]
Gumball: What was that?
Darwin: A twig.
[They continue walking again. A flapping sound is heard]
Darwin: What was that?
Gumball: That's my butt cheek quivering with fear.
Gumball: Yeah. Look.
[Gumball's butt is seen quivering. Then some of Kenneth's goo drops on them. He growls, and the Watterson brothers scream and run. Kenneth growls again, and pounces on the ground. He gets stuck in the fence]
Gumball: Darwin, this is our chance!
[They charge, and repeatedly smack Kenneth's butt with their weapons. But each time they hit it, someone inside Kenneth screams "ow." The brothers notice this, and gasp with joy]
Darwin: Are you all right in there?
Richard: [Presses face against Kenneth's butt] Partly digested and a little cramped, but otherwise fine. Just get us out of here, please!
[Kenneth gets up, and sends the brothers flying. They hit a wall]
Gumball: [Groans] Dude, we gotta do something.
Darwin: I got it!
[Darwin grabs the garden hose, and eventually ties it around himself]
Darwin: Tie the hose pipe around me, then all I have to do is dive into his mouth, grab everyone, make a human chain, and when I say, "okay," you simply pull us out. Got it? Let's go!
[Darwin runs to Kenneth, and successfully gets eaten. He sees the other people inside]
Darwin: Yeah! Did it! Everybody, hold tight. Okay, Gumball, now pull!
Gumball: Gotcha! [Struggles to pull them out; fails] Okay, this isn't working.
Darwin: Well, think of something else! Our lives depend on you!
Gumball: Uh, I hate to tell you this, but I got nothin'.
[Kenneth roars at Gumball, knocking him against the wall. He also turns the tap on with his impact, and Kenneth starts to bloat]
Gumball: No, no, no! Kenneth, please don't eat me! Please! If you like eating people, I-I'll bring you some, like a good mother.
[Kenneth continues growing with water]
Gumball: And, uh, maybe a salad once in a while because you're starting to get a little bit chubby.
[Kenneth pops, and the water inside of him floods the backyard. Gary floats by Gumball, and hands him a package]
Gary: Here's your package. Have a nice day. [Floats away]
[A pigeon floats by, and the flood recedes. The rest of the Wattersons are by his side]
Darwin, Anais, Nicole and Richard: Gumball!
Darwin: Great idea, turning on the hose.
Gumball: Oh, pfft. It was nothing. Just quick thinking, you know? I-I work best when I'm under pressure. It definitely wasn't an accident or anything.
[Kenneth (back to his small size) is seen. Gumball and Darwin walk to him]
Gumball: Aww, Kenneth. Look at you now. You're as sweet as when you were born. Who could imagine he'd turn into such a—
Richard: [Charges at Kenneth with a tool for a weapon] Aah!
Gumball: Dad, no!
Richard: Are you kidding me?! That thing ate me and barfed me! I'm gonna end this right now!
Gumball: B-But he didn't mean it. It's just that we've been bad parents!
Anais: Gumball, that thing is a man-eating monster!
Gumball: Yes, maybe he eats people once in a while, but maybe, just maybe, he needs some love and understanding. We are responsible for the future generation. We make the children that will become the world of tomorrow. Don't blame Kenneth. Blame yourselves, because you're my parents, too.
Gumball: Look at him. He won't hurt anyone now.
Darwin: Doesn't this poor creature deserve a second chance?
[Everyone observes him "innocently" looking around]
Anais, Nicole and Richard: Aww! Okay.
Gumball: Trust me, guys. This time, it'll be different.
[Skips to a gigantic Kenneth wreaking havoc on Elmore town. Sirens blare, and helicopters train their lights on Kenneth. Kenneth knocks a helicopter down, and roars]
Darwin: On second thought, we probably should have listened to Dad.