One day, the Action League returns to Action Headquarters after a routine patrol, only to find the ultimate indignity; someone covered it in toilet paper. To add insult to injury, they used Stinky Diver's private property to do it! The Flesh sympathizes with Stinky, because he knew that he was saving that roll for a special occasion. He asks who could be so mean to do so, and Meltman points out a mysterious ninja lurking in the shadows. The ninja tosses one of his stars at Stinky, but Stinky ducks and the star hits Meltman. Thundergirl reads "The Red Ninja" logo on the star. Stinky realizes that after all these years, the Red Ninja has come back for his revenge.
Stinky Diver tells the League about when he and the Red Ninja first attended Kung Fu Jr. High. They were both sparring for their tutor, Master Pu. Red was always a sore loser, and tried tossing his stars at Stinky, only for him to hit Master Pu instead and get detention from him. He vowed that he would get revenge on him someday. Thundergirl assures Stinky that now he has something he didn't before; friends who will stick by him in his time of need. Stinky tells her, The Flesh, and Meltman that the Red Ninja is a ruthless killing machine. Upon hearing this, The League backs away, leaving Stinky to fight The Red Ninja by himself.
With a showdown on the way, Stinky Diver goes to Master Pu's house, to gather some forgotten fighting tips from him. When he arrives at Master Pu's house, Master Pu asks him if he's forgotten all his training, and tells him two very important tips; #1: Always bow when addressing your master, and #2: never take your eye off your opponent, the latter he tells him while kicking him. Master Pu tells Stinky that the years have made him as soft as a bean curd, and that in order for him to battle The Red Ninja, they must begin training immediately.
Master Pu and Stinky begin their first exercise at a grill (complete with burgers and hot dogs being cooked), where Master Pu tells Stinky, "Only in your mind, does the fire burn" as Stinky walks across the grill's hot surface. Stinky's next exercise takes place at Master Pu's house, where Master Pu tells him, "Only in your mind do the blows sting", while hitting Stinky repeatedly with his staff. Stinky's third and final exercise is trying to karate-chop a brick in half, where Master Pu tells him, "Only in your mind does the brick cause you pain". A bunch of nearby bricks fall on Stinky as he tries to karate-chop his brick in half.
After all their training, Master Pu assures Stinky that he is now ready to fight the Red Ninja. Stinky, who appears injured with many casts and crutches, tells Master Pu that the only thing he's ready for is the Emergency Ward. Master Pu tells Stinky that the Butterfly does not need wings to fly. Stinky tells him, "Yes, it does." Master Pu tells Stinky he was speaking metaphorically, then tells him to go out and battle the Red Ninja.
Later that day, in the Kung Fu Village, the Action League are sitting on bleachers, cheering for Stinky, and jeering at the Red Ninja. The Red Ninja tells the injured Stinky that he looks as bad as he smells. Stinky tries to fight back, but one of his arms falls off as a result of Master Pu's training. The Red Ninja tosses one of his stars at Stinky, but Stinky ducks, and the star hits Meltman. The Red Ninja then grabs Stinky's fallen arm and starts beating him with it. The Narrator asks the viewers if Master Pu's training will save Stinky, or if the Red Ninja will win the battle, then tells the viewers to stay tuned for Part 2.
In the second act, just as it looks like The Red Ninja is about to defeat Stinky, Stinky thinks about what Master Pu would say in this kind of situation. Master Pu tells him in his mind, "The quills of the porcupine must sometimes flutter through the air.". Stinky has no idea what that means, so Master Pu tells him in his mind, "Use your spear gun, idiot!". Stinky pulls out his spear gun and shoots at the Red Ninja, knocking him off the table, and landing on the floor, where he gets sucked up by a vacuum cleaner. The Action League cheers for Stinky at his victory, and Master Pu hands him his arm, telling him he salutes him now that he's won. Stinky, ungrateful for Master Pu's training, kicks him into a pot, where vegetables are being steamed. Stinky then tells Master Pu, "Like you always say, never take your eyes off your opponent, Master Pu!", and he and the rest of the league laugh as the episode ends.
- Narrator: "Ninja, returned. Stinky Diver, learned. Master Pu, concerned."