[Episode starts on a rainy night. In his lab, Falco is trying to recreate the project. All of the rats are in their cages as Falco lamented himself as he picked up a vial.]
Falco: They all thought they could stop me. The corporate fools who pulled my funding. The scientific community who shunned me. Those turtle freaks who thought they got the last of my mutagen. But they were wrong. Even with this tiny amount and nothing but these disgusting sewer rats to experiment on, I have nearly recreated my psychic neurochemical. And when I do, the shortsighted idiots who rejected me will tremble before the power and genius of Dr. Victor Falco.
[The rats that were above the ceiling bit out the wire setting of an explosion. Falco becomes critically injured as he holds his head, he then calls the rat with his extrasensory abilities.]
Falco: No, no! Help me! Please! Help! Help!
[The rats started to come to him. The man smiles evilly and cackles. He is now born as the Rat King.]
[theme song]
[At the dojo]
Leo: Okay, here's the plan. Donnie, you're going to strike first.
Donnie: No, wait. You want me to come at Splinter? I'll get pummeled.
Raph: Well, getting pummeled is your specialty.
Leo: Trust me. It's all part of my plan to catch Splinter off-guard.
Mikey: Uh, Leo, don't take this the wrong way, but against Splinter, your plans always get our butts whipped.
Leo: Okay, new thought. Mikey, you attack.
Mikey: He took it the wrong way.
Raph: Enough talk. Let's do this.
[Slow motion begins as Mikey tries to kick Splinter, but Splinter grabs his legs and kicks him to the ground. Donnie tries to attack him, but he kicks Donnie to Raph. Splinter notices Leo, tries to hit him, but Leo dodges attacks and punches Splinter in the face. Leo becomes shocked and horrified by hurting his master.]
Leo: Ah! Sensei, I'm sorry.
[Leo gets pinned down.]
Donnie: Oh, man. Leo's a goner.
Mikey: Oh, nodie dodie.
Splinter: [impressed] Well done, Leonardo. But just when you had the advantage, you hesitated, and that made you vulnerable.
Leo: [getting up] Hai, sensei.
Splinter: Now, that is all for today. Unless you care for a rematch.
Donnie: No, thanks.
Mikey: I'm good.
Raph: Yeah, I think we're all set here.
[Splinter leaves into his bedroom.]
Mikey: Leo!
Raph: Not bad.
Donnie: Dude, I can't believe you actually tagged sensei. That was epic.
Mikey: The hand that punched Splinter. You know, you can never wash this again.
Leo: I gotta say, guys, it was all teamwork. We are definitely getting better.
Donnie: Think we might be catching up to Splinter?
Mikey: Yeah, maybe soon, we won't need him to train us at all.
[Unbeknownst to them, their sensei overheard their conversation and is saddened and perturbed.]
[Meanwhile at the rat king's lair]
Rat King Falco: Through your eyes, brothers, I finally see the world for what it really is. This city is infested. Scrambling around in their pointless lives, spreading disease, forcing us to live in the shadows, like vermin. No more. They are the true plague. Together, we shall rid this city of humanity and reclaim it for ourselves. And no one, not even those vile turtles, shall stand in our way.
[From around the city, the rats started to roam New York frightening people. Humans started to leave Murakami's place and a few climbed on top of police cars.]
Police officer: Oh, that's disgusting.
Carlos: Citizens are fleeing the city in droves, but authorities say that while the rash of rodent activity is unusual, it's no cause to get rat-tled. For channel six news, I'm Carlos Chiang o [rat attack him and some more] holy moley! Get them off me! Get them off-
[The camera goes off. April was walking down the street and saw a small rat.]
April: Aw, hey, little fella. Where's your mama? [she saw the rat horde] Sorry I asked.
[She drops her groceries and runs away from the rats.]
[From below the Rat King's lair.]
Rat King: You've done well, brothers, but our fight is not yet won. Those turtles are still out there, and I fear that even you may not be able to stop them. But I sense a kindred spirit who can. A fellow rat, who once knew the bonds of humanity as I did. A great warrior, who shall serve as both my eyes and protector. Join me, join me!
[The turtles hear Splinter's pained scream and enter the dojo.]
Donnie: Sensei, are you okay?
Splinter: I am fine.
Leo: Are you sure you're alright? You don't seem-
[Donnie's cell phone rang.]
Donnie: Hey, that's April's ringtone. [answers it] Hey, April. I mean, hey, April. I mean-
April: Donnie, stop talking. I need some help. I'm having a little bit of a pest problem.
[April is on an electric pole, trying to avoid the rats. Outside, The turtles ran across the rooftops.]
Mikey: Oh, wow, the city is so beautiful in the daytime. Except for the, you know, billions of rats.
Donnie: Actually, the entire rat population of New York is only about thirty six million, which-
Raph: I will smack you out of your shell.
Leo: Uh, guys, we may have a problem.
[They looked down and saw thousands of rats where April is.]
Mikey: Oh, rats. Get it?
Raph: For the fourteenth time, yes.
Donnie: We're coming, April! Don't go anywhere!
April: Where could I possibly go?
[Leo and Raph used their grappling hooks and swung down on the pole. Mikey and Donnie went next. They start to climb to the top.]
Raph: These stupid rats are starting to get on my nerves.
Donnie: Rats aren't stupid. Despite their small brain size, they're remarkably- [rat falls on him] Ow!
Leo: I warned you. Raph, put down the rat and keep climbing.
April: Hurry!
[They continued as the pole began to tip with the rats biting it. April begins to fall. Donnie catches her.]
Donnie: Gotcha! Whoo-hoo! As long as Donnie's here, you have nothing to- Oh, boy.
[The rats gnawing the pole break loose. Everyone screamed and hung on.]
April: Okay. I appreciate you guys coming to help, but how is this better than getting eaten by rats?
Mikey: At least it'll be quick. With rats, they chew and chew and chew and chew and chew-
April: Okay, we get it.
Donnie: Let's move. Hurry.
[They carefully began to climb on top. The pole snaps, flying the teens to the other side of the rooftop. A loud crash made all the rats squeal, seemingly killed.]
Leo; Chew on that, rat finks! Oh, come on. That sounded cool.
April: Does anyone know what the heck is going on?
Donnie: I'm not sure. But whatever it is, this attack is extremely well coordinated. Obviously, there is a higher intelligence at work here.
Raph: Well, that rules out Mikey.
Donnie: I'm serious. Someone or something is controlling every rat in the city.
Raph: Wait a sec. Every rat?
Leo: That means that Splinter could be-
[In the dojo]
Rat King: Why fight it? You know in your heart you belong with the Rat King.
Splinter: Leave me. I am not one of your rats to control.
Rat King: You're right. You are so much more. We are so much more. And together, we will be unstoppable.
Splinter: No. You and I are nothing alike.
Rat King: We've both lost all we held dear. We've both become outcasts from society. And we've both come to see the world through the eyes of rats.
Splinter: No. I am a man. I am Hamato Yoshi.
Rat King: Not anymore.
[April and the turtles arrive to see Splinter lying down on his back.]
April: Is he okay?
Raph: Donnie, you're the smart one. What do we do?
Donnie: Maybe we should poke him.
Leo: Good idea. Mikey, poke him.
Mikey: No way, I'm not poking him. You poke him.
Leo: Okay, we'll put it to a vote.
Turtles: Mikey.
Mikey: I want a recount.
[Donnie gives Mikey his bo]
Mikey: Fine.
Donnie: Easy, easy. Careful not to squeeze the-[spear suddenly activates]
Turtles: Aahh!
[Mikey drops the bo before Donnie picks it up and gives it back to Mikey.]
Donnie: Okay, let's try it from the other end.
[Mikey shakes his head but Donnie pushes him forward. Mikey pokes him carefully.]
Mikey: Whoa, he is totally out of it. Dudes, check out the nose nuggets.
Rat King: We have evolved beyond humanity. We have no need for them, but we can help each other. Join me, and you shall hide below the surface no more.
Splinter: No.
Mikey: Michelangelo is awesome. He is the smartest, handsomest, butt-kicking-est of all my-
[Mikey gets thrown while Donnie and April dodged him.]
Mikey:.... sons..
Leo: Sensei, are you okay?
Splinter: No, Leonardo. I am not. It would appear that your former adversary, Dr. Falco, has returned.
Donnie: Falco's behind this? How is that possible?
Splinter: Somehow he has acquired a telepathic connection with every rat in New York. And he now calls himself the Rat King.
Mikey: [annoyed] Oh, great. So now we're letting the bad guys name themselves? We gotta take him down.
Splinter: Yes, Michelangelo, you do. The Rat King will not rest until he has total control of this city and my mind.
Leo: Sensei?
Splinter: Everything I knew is gone. My wife, my daughter, my clan, even my humanity. You four are all I have left.
Raph: Don't you worry, sensei. We'll stop him.
Donnie: But we gotta find him first.
Splinter: When the Rat King attempted to take control of me, I could see into his mind. You will find his lair in an abandoned utility junction beneath Herald square.
Raph: Let's go play exterminator.
[Splinter cries in pain.]
Leo: Fight him, sensei.
Splinter: I will. Just hurry.
April: It's okay, guys. You go after the Rat King. I'll stay with sensei.
[Leo looks at the photo. In the sewer.]
Mikey: What's going to happen to Splinter if we can't stop the Rat King? Which, by the way, lamest villain name ever.
Donnie: Let it go already.
Raph: We're going to stop the Rat King, and Splinter's going to be fine. Right, Leo?
[A small mouse ran past them.]
Donnie:[quietly] Shh, quiet. Do you guys hear that?
[A massive horde of rats appears.]
Raph: You gotta be kidding.
Mikey: Aw, ra-
[Raph covers Mikey's mouth.]
Donnie: Uh, Leo, any ideas?
Leo: Just one. Move!
[They run as the rats chase them. They managed to grab onto the pipes. Mikey shook a few rats off as one bit his head.]
Mikey: Oh, no. They've got the taste for turtle now.
Leo: Come on. Just keep moving.
[They carefully climb past the wave of rats.]
Rat King: Why do you cling so hard to this life of yours?
Splinter: I am needed here.
Rat King: By whom? Even your so-called children have begun to outgrow you. And soon, you will be all alone. Come, we are your family now.
Splinter: No!
[April checked inside the dojo and saw that everything got foggy.]
April: Master Splinter?
[April turned around and saw Splinter, his eyes red. She drops the bowl in horror. She starts to dodge as Splinter attacks.]
April: Master Splinter, wait! It's me!
[Splinter pointed his sword and charged at April.]
Rat King: Come, my brother. Come to me now.
[Splinter begins to leave April. April sighed in relief.]
April: Bangs were a little long, anyway.
[The turtles are still climbing on the pipes.]
Mikey: I'm just saying, I can think of a million better names than the Rat King. There's Ratzilla, the Verminator, Lord Rattington-
Leo: Can it, Mikey. We're almost there. The utility chamber should be on the other side of that wall.
Raph: Uh, you mean that disgusting, furry, squirming wall?
[They looked and saw thousands of rats covering the tunnel.]
Donnie: How are we supposed to get past that?
Leo: Raph, those barrels. Ventilate 'em.
Raph: You got it.
[He throws ninja stars, causing oil to leak.]
Donnie: Uh, Leo, you do realize those chemicals are highly combustible.
Leo: You don't say.
[He cut an electric wire and caused a massive explosion, killing the rats offscreen.]
Leo: Let's move.
[The turtles arrive at the Rat King's lair.]
Rat King: Ah, my turtle friends, we meet again.
[A white rat appeared on his shoulder.]
Raph: Except last time, Falco, you weren't wearing a sad Halloween costume.
Rat King: I am the Rat King!
Mikey: Lame.
Leo: Sorry, we don't have any treats for you. But we've got a few tricks.
Raph: Way to ruin the moment, Donnie.
[Donnie answers his phone.]
Donnie: Uh, April, now's not really the best time.
April: Donnie, it's Splinter. He's gone.
Donnie: What do you mean, "gone"? Gone where?
Splinter: [brainwashed] Here.
[Brainwashed, Splinter enters and glares angrily and seriously at the turtles. The turtles gasp in shock and horror, wide eyed by seeing their sensei brainwashed.]
Leo: What's wrong with him?
Donnie: It's like his brain is completely turned off.
Others: You mean like Mikey?
Mikey: Dude, you are so predictable.
Leo: Sensei, snap out of it.
Splinter: [brainwashed] You waste your words. This is where I belong, with my brothers.
Rat King: He is mine now. Imagine my delight when I realized that controlling your master would not only make me invincible, but would also be the key to your demise. Splinter, destroy them.
[Splinter begins to step forward.]
Leo: Sensei, DON'T!
[Splinter stops. Falco takes off his bandages and hat to reveal a corpse-like face and forces Splinter to attack.]
Donnie: Are we really going to do this?
Raph: Remember, we did beat him once. Kind of.
Leo: Yeah, and we can beat him again. We can do this, guys. Do not hesitate. Take sensei down.
[They charge at Splinter. But Splinter dodged and knocked them into different directions.]
Donnie: I just had a horrible realization. He's been going easy on us all these years.
[Donnie goes forward and tries to attack. Splinter discharged his bo and knocked him.]
Mikey: Donnie!
[Mikey throws his kusari chain. but Splinter catches it with his sword and tossed the orange turtle aside.]
Raph: Nobody hits Mikey but me.
[Splinter backflips and knocks him out. Leo is the only one standing.]
Leo: Sensei, please.
[Leo starts to attack Splinter. He loses his swords and gets easily defeated.]
Leo: Wait.
Rat King: Finish him.
Leo: Remember who you are, Hamato Yoshi. Donnie, Raph, now!
[The turtles pinned him down.]
Leo: Please, father. We need you.
Rat King: Don't listen to him, brother. Your place is with me.
[Splinter knocks the turtles down and pinned Leo. He breaks free until he finally snaps out of it.]
Splinter: My place is with my sons.
[He used the final blow and knocked the Rat King down.]
Turtles: Sensei!
[The rat plague began to take Falco away.]
Mikey: And that's the last we'll see of Count Ratula. Yeah, all right. It's Rat King. But I'm naming the next one.
[At the dojo.]
Leo: Sensei, are you sure you're okay?
Splinter: I am fine, thanks to you. You did well, my son.
Leo: Well, you did hesitate, and hesitation leads to vulnerability.
Mikey: We did pretty good, too, huh? Yes.
Splinter: I am proud of you all.
Leo: Who knows, maybe one day we'll be even better martial artist than you.
Splinter: Remember my son, everything you know I've shown you. [Grabs Leo and throws him into a wall] But I have not shown you everything I know.
Leo: It's great to have you back, sensei.
[Splinter watches him in satisfaction as the rest of the turtles smile in amusement as the episode ends.]