Preview: Donatello narrates as we open with April in her shop. O'Neil takes a box outside to the trash, but someone else is out there, too, waiting for her. The shadowy figure attacks!
Act 1: Open with the Turtles outside April’s shop. As they enter, the ninjas hear people fighting in the back alley. The TMNT hurry to see what's going on and they find April holding a baseball bat over her defeated attacker. The Turtles turn on the street light and reveal the mugger to be Casey Jones. April is furious, but Jones explains that she asked him to do it when she was talking about how well her training with Master Splinter was going. Although April handled the situation well (and, fortunately for Casey, she was only wielding a whiffleball bat), she's still mad at Jones and invites the Turtles in for some tea - purposely slamming the door on Casey's face as they go inside.
The Turtle make themselves comfortable as O'Neil makes the tea. Donny gets another call on his Shell Cel that turns out to be a Fax. April brings the tea to the table and everyone sits down. April is disappointed in her abilities, as she believes that she should have heard Casey before he started to rush her. The TMNT explain that it takes a lot of practice to gain total readiness, and April asks if they'll teach her. The mutants look aghast and quickly refuse, which surprises O'Neil. The guys explain that they tried to teach someone once - and it did not go well.
Dissolve into the past where we see the much younger Turtles (Turtle Tots). Master Splinter is repeatedly warning his students to never go to the surface. Disobeying their Sensei, the Tots decide to see what’s topside at their first opportunity. As the young ninjas enter an alley and marvel at the beauty of the surface world, they see two goofy looking human boys and quickly hide. The boys are Arnie and Stevie, and they look troubled. A group of bullies are playing street hockey in front of Arnie's apartment. Stevie tells his friend that he'll help him stand up to the thugs, but Arnie tells his buddy to go home and he'll take care of things. A much relieved Stevie departs as Arnie tries to get into his apartment. The roughnecks notice Arnie and surround him, demanding that he pay a toll for walking on their turf.
Act 2: The roughnecks chase Arnie into the alley where the Turtles are hiding under a dumpster. The bullies begin to beat Arnie with their hockey sticks and the mutants decide to help. From various hiding places, the Turtles use trash and clotheslines to turn the roughnecks against each other. Finally, one of the hoodlum's mother calls and the bullies depart. The Turtles decide that they should teach the boy how to defend himself. Leo dons a disguise and offers to help the kid learn how to fight. Leonardo leads Arnie to the rooftops, where they sit in the lotus position. Leo tries to teach the boy the importance of focusing the mind. Unfortunately the lesson gives the boy a headache and the position makes his legs go numb, but he tries his best to obey Leo's instructions.
Cut to the Turtles Lair. As the Mike and Don are training, Splinter announces that it’s Leo’s turn - but Leonardo is still topside. Raphael is sitting on the couch with a stuffed animal wearing Leo's bandana - which from Splinter's viewpoint appears to be Leo. However, when the Sensei calls for Leonardo to take his turn - he doesn't answer. Mike and Don try to distract their Master, and Raph waves the stuffed animal's arm to try to fool the rat, but Splinter is suspicious and closes in on the couch...
Act 3: Open as Splinter is about to grab the stuffed animal disguised as Leonardo. But just as he’s about to grab it, Leo turns around, revealing himself. As he gets up, we see that the young ninja was sitting on the stuffed animal - somehow he managed to get back to the lair in the nick of time.
Back on the rooftops, Mikey teaches Arnie that the most important thing is to have a cool battle cry that will instill fear in his enemies. Mikey gives the boy a battle cry, but he can't remember it very well. Mike then takes Arnie down to the alley and pushes him toward the bullies, who are playing street hockey. The boy tries out the battle cry, but he can't remember it. The roughnecks are anything but intimidated and they rush forward and beat up Arnie.
Later, Donatello is trying to teach Arnie how to play chess, so he can learn to plan his strategies ahead of time. Arnie struggle with the complexity of the game and Don departs. Raphael arrives and tells Arnie that the only important thing is having a good weapon. The boy complains and wishes that his mentor would make up his mind on how he should behave. Raph ignores the complaint and grabs the chess pieces. The Turtle sets up some cans and tosses the game pieces at them , knocking them all down. Raph hands Arnie some chess pieces and tells him to give it a shot. The boy throws the game pieces, but they hit the ground, rebound off the wall and come back to pelt the youths. Undeterred, Raph leads the kid back to the streets and tells him to attack his enemies. Arnie hesitates, but approaches the thugs and throws the chess pieces at them. The projectiles miss by a mile, and the roughnecks once again attack and beat the boy.
Back at the lair, Splinter resumes training and tell his students to pair off. The Sensei then notices that Raphael is absent. The Turtles make up a story that Raph is in the shower, but Master Splinter is very suspicious now. The young ninjas rush off to get Raphael, who is just returning. The guys douse Raph with a bucket of water, explaining that he's supposed to be in the shower. This treatment angers the young Turtle, but just ten Splinter appears. The tots try to convince their Master that Raph really was taking a shower, but Splinter is dubious since Raphael is still wearing his bandana.
Later, all four Turtles are in the alley (but only one Leo is disguised and visible).Leonardo urges Arnie to take all that he's learned and fight the bullies. Arnie complains that he's already been beaten up twice, but Leo prods him into trying. Of course, Arnie takes another beating. At this point, the Turtles discover that none of them have taught him anything about fighting as they all thought the others were doing that. Just then, a very angry Master Splinter arrives...
Act 4: As the Turtles turn to see the shadow looming over them, they spy their furious Sensei. Splinter angrily orders the Turtles back to their lair. The lads protest, saying that they have to help the boy, but Splinter states that they do not know enough to teach and the child must find his own path. With that, the Turtle tots return to their lair, never to see Arnie again.
Cut back to April's apartment in the present where everyone shares a laugh. The Turtles recall that Splinter was so angry that he made them workout for 18 straight hours. April wonders what became of the boy, and the ninjas explain that they don't know...
Back in the past, we see Arnie walking alone down the sidewalk. As the boy approaches his apartment building, he sees his nerdy friend Stevie getting bullied by the same group of thugs that have been beating him. As the roughnecks taunt his friend, Arnie becomes incensed. The boy goes into a rage and attacks the bullies - first punching their leader in the jaw and knocking him flat and then grabbing a hockey stick and pummeling any others that try to fight him. The rest of the hoodlums flee in panic as Arnie sneers that they'd better run. Once the battle has been won, Arnie stands victorious in the middle of the street and tries out his battle cry - which morphs into "Goongala!" (thus we discover that Arnie is actually Arnold "Casey" Jones). Stevie is impressed with his friend's newfound fighting skills, and the two buddies walk off, finally feeling confident and safe.