Quack Quack is lying on his stomach on the ground with an open mouth while Stumpy tries to hit golf balls into his mouth. Stumpy, as usual, is terribly bad at it, and he can't hit the ball into Quack Quack's mouth. After several unsuccessful tries, Quack Quack gets fed up and chases the ball. He dives into the air and catches it, only to fall off a cliff. Stumpy rejoices over his victory when Kaeloo shows up and asks what they're doing, and he says they're playing mini-golf and invites her to join, with Stumpy taking Quack Quack's place.
After the episode's title card is shown, the scene cuts to Kaeloo trying to get Stumpy to cough out the ball (which he apparently inhaled when Kaeloo hit it into his mouth). Quack Quack tries playing hide-and-seek with a yogurt (which really doesn't work since it can't move), and Mr. Cat sneaks up behind him and hits him with a giant mallet. Kaeloo is about to yell at Mr. Cat when she realizes that there's a zit on his face. Kaeloo and Stumpy try to touch it, but Mr. Cat threatens to (literally) kill them if they touch him.
Suddenly, Mr. Cat has a huge outbreak of acne on his face. Kaeloo is horrified, since this means that he is probably now a teenager. Quack Quack and Stumpy bid farewell to the cat, who questions the purpose of this. Kaeloo explains that the encyclopedia of Smileyland's rules states that Smileyland is open only to children. Mr. Cat refuses to believe it, and Kaeloo concludes that he is definitely a teenager since "teenagers don't believe anything", so she hands him a suitcase and pushes him towards the door.
He still refuses to leave, since Smileyland is his home, and suddenly his legs disappear. Kaeloo explains that he is starting to disappear since he no longer has a place in Smileyland. He claims not to be a teenager, sucking his thumb to show how "young" he is, but it doesn't seem to be working. He asks if playing games can help fix the problem, and Kaeloo suggests jumping rope. Mr. Cat refuses (since he believes jumping rope is for girls), but quickly changes his mind when his tail disappears. He jumps rope with Stumpy and Quack Quack turning the rope, but unfortunately he gets hit by the rope.
He asks for a different game, so he and Quack Quack have a staring contest where the first one to laugh gets hit on the head. He hits the duck on the head with a mallet and proclaims victory, claiming that Quack Quack laughed. Kaeloo reprimands Mr. Cat for mistreating Quack Quack when the latter is clearly trying to help him. Mr. Cat's torso disappears and only his head is left.
They try playing volleyball, but unfortunately, Mr. Cat completely disappears before he can hit the ball. Stumpy cries, begging Mr. Cat not to leave him, and Kaeloo says that she'll never forget him. Quack Quack points out that Mr. Cat never stopped tormenting him, and Kaeloo is about to tell Quack Quack about her feelings for Mr. Cat when she notices a zit on Stumpy's face. The latter vehemently denies it being a zit, but he has a sudden outbreak of acne (like the one Mr. Cat had earlier), and he is horrified. Quack Quack asks if there is a vaccination to prevent teenage, when suddenly a mallet mysteriously floats in the air and hits him on the head. It turns out to be Mr. Cat, who is now completely invisible. He announces his plan to torment Quack Quack all the time and escape unpunished, and Kaeloo angrily transforms. However, Bad Kaeloo cannot find him since he's invisible (and constantly moving), and he even manages to kick her.
Later, Mr. Cat is chasing Quack Quack with a chainsaw and Stumpy, now just a head, is excited to have almost attained invisiblity. Kaeloo reads through the book to see if there is any way to bring Mr. Cat back to normal, and she finds out that there is a disease in Smileyland that causes zits to randomly appear all over the person's face, sometimes accompanied by invisibility - and it's temporary. She realizes that Mr. Cat and Stumpy haven't hit puberty yet, they're just sick. She then transforms and grabs a jump rope, jumping while waiting for Mr. Cat to recover from the disease.
Mr. Cat is cured and re-appears, to his horror. He tries to run, but Bad Kaeloo grabs him with the jump rope. She then uses it to slam him into the ground multiple times. Quack Quack calmly ignores Mr. Cat's pleas for help, and the now-invisible Stumpy decides to play hide and seek with Quack Quack. He recovers from the disease, and Quack Quack finds him. Stumpy realizes that he can also see himself, and rather than realizing that he is visible again, he concludes that he now has the power to see the invisible.
- Quack Quack
- Mr. Cat
- This episode reveals that all four main characters are still children and have not reached teenage yet.
- This episode reveals that teenagers are not allowed in Smileyland.
- There is a disease in Smileyland that causes the person to have zits appear all over their face and (in some cases) turn invisible.
- This is the first episode to have a character's name in it.
- When Mr. Cat's legs disappear, Stumpy, who is now taller than him, compares their heights; this would later become a running gag in Season 2 with Olaf.