[It all started in Baxter's office, trying to figure out how to work on mutants. Shredder walked in with photo’s while tossing them aside.]
Shredder: Baxter Stockman. I ordered you to build me a mutant army, and you give me this?
[Shredder threw some photos at Stockman. Stockman picks up a picture of a duck.]
Stockman: No, no. Don't you see? It swims, flies, and know Tae Kwon do. It's a triple threat. [Stockman freezes as Shredder's blades slashes the photo into pieces with quick ease.] And it quacks?
Rahzar: Can it, Stinkman. [walks up and snaps his jaws] This is the last time you mess up.
Stockman: Mess up? But look at you, Rahzar. You're twice the dog, uh, man you were before.
[Rahzar growls]
Shredder: No, Bradford. I have a more suitable fate in mind. You have failed me too many times.
Stockman: No! I mean, please, Master Shredder. I've got plans, huge plans. Mutant pigs and rhinos-
[Shredder throws the kart on the floor.]
Shredder: Pigs?
Stockman: [weakly] And rhinos.
[Shredder. having none of Stockman's antics, pulls out a joy stick.]
Stockman: What are you doing? No! The mutagen? You can't. I wouldn't be of any use to you as a mutant. Please, don't.
[Shredder presses the button on the joystick. and the collar on his neck activates.]
Shredder: I am not a man of idle threats.
Rahzar: Heh, bet you'll end up a bigger freak than me, Stinkman.
Stockman: There's nothing wrong with idle threats!
[He tried to get it off but nothing happened as a fly landed on his nose. Baxter opened his eyes as Shredder and Rahzar leave.]
Stockman: Yes! Oh, thank you, thank you, thank you, thank you, thank you.
[The mutagen vials on the collar breaks, causing him to slam to the wall. Stockman, covered in mutagen and sobbing, starts to mutate.]
[Theme song]
[At the lab, Donnie is making an antidote.]
Donnie: Almost got it. Almost got it.
April: Are we done yet, Donnie? We've been up for, like, a million hours. [Yawns.]
Donnie: Oh, no, no no worries, April. This time, it's gonna work. We'll finally be able to turn your dad human again. Now I'm adding a sample of your DNA. [Chuckles.] So brace yourself. For the scientific breakthrough of the century! Retro mutagen!
[April is asleep. Donnie began to put the liquid on the disk and began to examine it.]
Donnie: Okay, mutant cells. Please turn normal. Please turn normal. Oh.
[The cells suddenly become normal,]
Donnie:[ Gasps.] Eureka. I did it! I really did it! Whoohoohoohoohoo! [Whoops.]
April: [waking up] You did it? You really did it?
[The rest of the turtles enter the lab.]
Leo: Did what?
Mikey: Invent pizza that doesn't get soggy in milk?
Donnie: I finally made it. Retro mutagen, you guys! The key to turning Mr. O'Neil human again. And you too, Sensei.
Splinter: Human once more? Save April's father first, and then I will consider it.
[Mikey picks up the beaker.]
Mikey: Ooh, what if I turned myself human again? I wonder what I'd look like. What up?
Raph: We were never human to begin with, genius. We'd just turn back into turtles.
Donnie: [grabs the vial] Give me that. I've only got enough for two doses, one for April's dad. And one for Master Splinter.
Leo: Can you make more of the stuff?
Donnie: Yeah, but it takes ten canisters of mutagen to refine just one tiny dose of Retro mutagen, and I don't have any left. But at least we can find your dad and change him back.
April: Oh, I'm just speechless. Thank you. Thank you so much, Donnie. You're the best. Muah!
[Donnie passed out from too much love in April. Meanwhile, Stockman's shadow was seen, he was not a human anymore. She shoved garbage out of the way and vomited a candy bar.]
Stockman Fly: What am I? [Buzzes.] I'm nothing anymore. I'm a freak. I'll never be taken seriously. As a scientist. Oh, wait. Wait. [Panting.] Yesss. Yesss. [Buzzing.] Stockman DNA....Combined with purestrain human DNA. [Buzzes.] I could be normal again. Better than normal. Twice the man Stockman was.
[Rahzar and a couple of footbots arrive]
Rahzar: Stinkman. Where are you? I want to see what you turned into. Come on out.
[Something pulled the cable and lights flickered.]
Rahzar: Scared to show yourself, Stinkman? It's not like you can get much uglier.
[Something scuttered in the room. Who or whatever is in there is nearby. One of the footbots got taken away when Rahzar turned.]
Rahzar: Show yourself, mutant.
[The figure slowly climbs up the ceiling and spits acid at Razhar. The creature started to fly away. Meanwhile, Kirby is trying to suck a billboard with a picture of a woman.]
April: Dad.
Leo: All right, April. Hang back. We don't want to rile up your dad like last time.
April: But I can help. I can calm him down.
Raph: Last time you tried that, he took you to his nest and tried to feed you dead rats.
April: Good point.
[Leo and the turtles take off using grappling hooks.]
Leo: All right. Got to do this, quick. Raph and Mikey, we can't let him escape. Donnie, spray him fast.
Stockfly: It's the Turtles! They're close. Now I have the power to squash them like bugs!
[They carefully approach Kirby. Donnie pulled out the shotgun and slowly aimed it at Kirby. Something buzzed making Donnie drop the gun. Kirby flies off.]
April: Dad, no!
[There Stockman was seen. He mutated into a house fly. His head has two bug-like eyes, mandibles, and antennas, his hair and his clothes remains normal. His hands have claws and he has wings.]
Stockfly: Sentimental humans. Give me the Retro mutagen. Now!
Leo: Another mutant?
Stockfly: Retro mutagen. Mine!
[He charged forward but Donnie grabbed him.]
Donnie: No! Get your claws off that vial.
[The mutagen falls and breaks. Angrily, Stockfly grabbed April.]
April: Let me go, you ugly germ farm!
[She punches him but Stockfly catches her.]
Stockfly: Silence!
Raph: I know who that is. It's Derek Stockboy!
Stockfly: It's Baxter Stockman! Come to my lab and you will bring more Retro mutagen, or the girl mutates with me!
[He flies off with April.]
Mikey: Wow, we really messed that one up.
Donnie: I only have one vial left. It'll take months to synthesize more.
Leo: Don't worry, Donnie. We'll get her back and make her dad human again.
Mikey: Let's hope so. Let's really hope so.
[Back at the lab., the turtles wait for Casey to arrive.]
Donnie: Aw, man, what am I gonna do? Save April and Mr. O'Neil. But what about Master Splinter?
Splinter: What about me?
Donnie:[Yelps.] Oh, um [Chuckles.] Hey, Sensei.
Splinter: Leonardo informed me of the situation. You must split up to rescue April. And to find her father.
Donnie:[Sighs.] I'm sorry, Sensei. This is all the Retro mutagen I have left.
Splinter: I may not be human, but I am fortunate enough to have my humanity. Save Kirby.
[Casey arrived at the lair.]
Casey: All right, who's the soon to be slapshotted goon. That kidnapped April?
Leo: Long story, Casey. We need your help big time. And yes, you'll get to hit someone with a hockey stick. Probably more than once.
Casey: Heh. Yes!
Raph: So you and me are bat wrangling tonight, Mikey.
Mikey: Aww, yeah! You know what that means, right?
Raph: Please don't.
[Mikey used a smoke bomb to change into his bug costume.]
Mikey: The return to Turflytle, dog!
Raph: You annoy me to no end.
Mikey: Buzz buzz is buzz back! Buzz!
[Meanwhile, Stockfly placed April in his lab.]
Stockfly: Stay!
April: Baxter, you don't have to do this. Donnie can help you. He can make more Retro mutagen. It'll only take a few months, I mean, hours!
Stockfly: [taking out a rope] If he fails, I have a backup plan.
April: So do I.
[April knocks him with her fan and tries to run but gets cornered by the fly.]
Stockfly: No escape!
[April is now tied up and hung over the vat of mutagen.]
Stockfly: You go here, and I press a button. You fall! and I- I jump in. We come apart and then we come together. You, me, as one. More human than I am now.
April: Baxter, listen to me. Dropping us into a vat of ooze isn't going to save you. You got to trust me on that.
[Stockfly spits acid and starts eating the candy bar..]
Stockfly: No! This is only way. Only way! Stockmanfly cannot trust anyone.
[The turtles and Casey arrive at the scene. Casey gets himself distracted by a fly and kills it, informing the mutant bug of their presence.]
Stockfly: Turtles! You tried, yesss. Tried to sneak in. No Retro mutagen, no trade.
Casey: I got your Retro mutajunk right here!
[Stockfly starts to spit acid on the rope, slowly breaking it. The mutant started to attack the turtles and Casey.]
Leo: Baxter, stop. Let us help you. We don't want to hurt you. Well, Casey does.
April: Ah! Um, guys? Little help here?
Stockfly: Not fast enough.
[The rope snaps in two and Donnie tries to save her but he misses as April falls into the vat.]
Donnie: April!
[Everyone watched in horror as April's form sinks into the ooze.]
Stockfly: Two become one!
Casey: Eat it, bug!
[Casey knocks Stockfly out. Leo and Donnie look down at the vat.]
Leo: Is she?
[April emerges from the Mutagen vat. She didn't mutate because she's a half kraang.]
April:[coughing.] Blegh, nice catch, Donnie.
Donnie: April! You're okay! But how did...? [gasps.] You're immune to mutagen! That's why your DNA worked to create Retro mutagen. Amazing.
Stockfly: I'll devour you all! I'll drink you like blobs of delicious filth!
[Mikey being chased by Kirby]
Mikey: Augh! Buzz buzz! Help me! Buzz buzz!
[Raph goes to the rescue.]
Raph: Got him on the run, Leo! Get over here before I let him eat Mikey.
Leo: No problem. We're on our way.
Donnie: Get your claws off of me!
[Rahzar appears]
Rahzar: I heard you say Retro mutagen. I can become human again?
Leo: On second thought, we might be a little late.
Rahzar: Bring me that vial.
[The footbots charged.]
Leo: Time to go!
[Leo used a smoke bomb and sliced the foot bots,]
Donnie: Back, you hideous arthropod!
Mikey: Give me Retro mutagen!
April: Get off of him!
[April attacks Stockfly. Casey then knocked the vial out of Stockfly's arms.]
Leo: We found April's dad. Let's get out of here.
[They begin to leave]
Stockfly: No escape! No escape.
[Superfly chases after them as Rahzar stabs a foot bot.]
Rahzar: Get me that vial before Stinkman uses it. That Retro mutagen belongs to me.
[Stockfly started to chase after the turtles.]
Casey: It's gaining on us!
Donnie: Firing garbage cannon!
[The cannons started to shoot but Stockfly caught it and eats it.]
Stockfly: Mmm, delicious.
April: Take a right! Now a left! Dad's this way. Whoaoa!
Casey: How do you know?
April: I just do. I told you I get certain feelings about things. Faster, Leo! Another right!
[They turned the direction. Meanwhile, Mikey is still being chased.]
Mikey: Raph! Kirbybat wants to suck. My turtle blood! Help!
Raph: Maybe I'll give him just a little taste.
Mikey: Raph!
Raph: I'm kidding. I'm kidding.
[Raph knocks Kirby down. April arrives as Raph and Mikey pull out the tarp.]
April: Wait!
Donnie: April?
April: Let me talk to him. Stay calm, dad. We're here to help you. Just calm down. Calm.
[Kirby had calmed down as Donnie held up the vial.]
Donnie: Sorry this took so long, Mr. O'Neil. Just a quick spray on your skin and you'll be good as new.
[All of a sudden, Stockfly scoops up the retro mutagen and flies off.]
Stockfly:[Buzzing.] I have it! Mine. Mine!
Donnie: Seriously? Again?
[The footbots appear flying in the air.]
Mikey: Flying footbots? Dude, this is getting out of control.
Leo: Let's move, turtles. [leaps onto a foot bot] Now, let's get that vial back.
Mikey: Turflytle and his sidekick maggot boy to the rescue!
Raph: Maggot boy! I'm gonna make you eat that stupid costume.
Donnie: April, you and Casey stay put and keep an eye on your dad.
[Donnie leaves]
Casey: You getting one of those feelings again?
April: Nope, just a bad idea.
[Stockfly is on the walls trying to open the mutagen.]
Stockfly:[mumbling] Stupid childproof cap.
Mikey: Taste the sting of Turflytle! Buzz buzz!
[Mikey knocks the mutagen out of Stockfly's grasp.]
Raph: Ha! Nice hit, tur. Er, Mikey.
[A footbot lunged at Raph and caused him to fall. Leo swoops down and sliced down the robots.]
Leo: You like that?
[April and Casey are riding Kirby]
April: Ha! Yes! Get him, dad! Knock him out of the sky!
Casey: So we're, like, riding your giant mutant dad? This is so weird.
[Donnie catches the mutagen.]
Donnie: Got it!
[The foot bot sliced off his rope, causing him to fall and grabs the mutagen. Donnie falls and tucks into his shell and crashes into a dumpster.]
[Casey grabbed his hockey stick.]
Casey: Swallow this, you ugly, goop drooling… Whoa!
[Kirby grabbed his stick with Casey holding onto it. Stockfly started to spit acid.]
April: Ugh, gross.
Casey: Catch up to him! He's getting away!
April: Oh, no, you don't! Get him, dad!
[Stockfly swoops down and steal the mutagen]
Stockfly: At last.
[He crashes onto a billboard and drops it.]
April: There!
[The mutagen begins to fall off the rooftop.]
April: Go, dad!
[the mutagen breaks onto the lamp post. April swoops him down and the mutagen lands on Kirby, Then the others cover him in a tarp. Casey and April come out of the tarp and watch. Kirby comes out, now human again.]
Leo: All right!
Donnie: Yes!
Mikey: Kirby's back!
April: Dad! I can't believe it. I missed you so much!
Kirby: A...April? What happened? Where am I? And why am I nude?
Mikey: Dude, when you hear what happened, you are gonna laugh so hard!
April: You did it, Donnie! You're the best of the best of the best! Muah!
Donnie: Two kisses in one day. Eat it, Casey Jones. Eat it! [Cackles.]
[Casey trips Donnie with his hockey stick.]
Leo: No sign of Stockmanfly. Add him to the list of stray, mutated bad guy freaks running around New York.
Mikey: Stockmanfly is Turflytle's ultimate superhero enemy, buzz buzz. But if he's out there, buzz buzz, I'll find him, buzz bu-
Raph: Enough with the buzz buzz!
Mikey: Okay.
Raph: Don't. Don't.
Mikey: Buzz buzz, dog.
[Raph yells in anger]
Donnie: I'm sorry, Master Splinter. I wanted to change you back. But I swear, if it's the last thing I do, I'll.
Splinter: Do not fret, my son. I am content with what I have become. I have no place in the human world anymore. This is my home, and you four are my family.
[The footbots dragged Stockfly to the lair.]
Rahzar: Well, look at you, Stink bug. I'd squash you right here, but Shredder has other plans for you.
Shredder: I have one last mutant I want you to create, or I will pluck your wings like the lowly insect you are.
Stockfly: Yes, master Shredder. [Buzzes.] Thank you for your generosity.
[He spits acid on a candy bar as the episode ends.]