- The Flesh
- Stinky Diver
- The Chief
- The Mayor
- Bill the Lab Guy
- Various Nuclear Reactor Employees
The episode begins at the Mayoral Mansion, where His Dishonor, The Mayor, has built a nuclear reactor, to give him free unsafe energy. He switches it on, and all his electronic devices power up.
Meanwhile, at the Mayor's nuclear reactor, Quarky, the daughter of Bill the Lab Guy, walks by on her way home from school. She wishes she could be a superhero like the members of the Action League, then she wouldn't have to go to school. Suddenly, an alarm goes off and nuclear waste begins to shoot out, landing on her.
At Action Headquarters, having heard about the nuclear disaster, The Action League are loading their luggage into the Action Mobile to evacuate from the neighborhood. Bill tells them that soon there will be nowhere in the world to run to. Once The Mayor's nuclear reactor blows, it will wipe out every living organism on the planet. The Flesh, completely missing the point of what Bill's saying, decides that they will have to go to Europe. The Chief tells The Flesh that they're not going anywhere, because they're going to shut down the nuclear reactor before it explodes.
Meanwhile, The Mayor is on the phone, planning to order some electronic devices from Smarter Image. Suddenly, an alarm goes off, and he sees the Action League, on their way to shut his nuclear reactor down, on his security camera. He flips a switch, which turns on a lawn mower, that chases after them across the neighborhood. They manage to escape from the lawn mower, or so they think. Suddenly, the lawn mower sneaks up in front of them and tears them to pieces.
Back at Bill the Lab Guy's laboratory, Quarky asks her father what's happening to her, as she hasn't felt the same after the nuclear reactor incident. Bill tries to comfort her by telling her she is going through puberty, meaning her body is changing in strange and wonderful ways. Suddenly, Quarky accidentally splits her father in half with laser beams shooting from her eyes. Quarky apologizes, but her father, although split in half, calmly tells her it's perfectly normal.
Back at the Mayoral Mansion, The Mayor is shredding all his unsafe nuclear reactor safety reports. Gunderson, one of his nuclear safety technicians, warns him that the water level is dangerously low, and if they don't shut the reactor down, it will explode. The Mayor ignores Gunderson and tells him he can have the rest of the day off. He turns on the waffle iron that Gunderson was standing in the middle of, which closes on him. The Mayor then sees the nuclear reactor out of control and the rest of his employees panicking on his securty camera, and decides to leave for Europe on his lawn mower. The Narrator asks the viewers if The Mayor's nuclear reactor will spell the end of the world, and since the Action League is in pieces, if anyone can stop it, then tells them to stay tuned for Part 2.
In the second act, with the fate of the Earth hanging in the balance, only Bill the Lab Guy can shut off the nuclear reactor. Unfortunately, there's nothing he can do. Quarky tells her father if there's anything she can do to shut off the reactor. She suddenly transforms into a superhero called Superteen, and flies onto the nuclear reactor. Bill is not happy with her and tells her to get down from the reactor, or she's in a load of trouble. This gives Quarky an idea. She looks at a sign, saying Unbalanced Load, and opens up the reactor. Inside the reactor, she tells her father that she found the problem. Bill, who is still mad at her, tells her she's grounded, whether or not she's a freakish mutant. Quarky tosses the stray slipper in the reactor onto him, then shuts the reactor off. The second the reactor is shut off, every one of The Mayor's electronic devices power down, including his lawn mower, which launches him into the road when it stops. The Mayor then gets run over by a car.
Moments later, the injured Action League in a badly-damaged Action Mobile arrive at the scene of the disaster and thank Bill for shutting off the nuclear reactor. Bill tells The Chief he didn't shut it off, his daughter did. Quarky then introduces her new identity, Superteen, to the Action League, saying she's a superhero, just like them. The Action League don't believe her, and think she's wearing a halloween costume and pretending to be a superhero. Quarky tells them her name is Superteen, and melts the Action Mobile with her laser eyes. The Action League now believe her and agree to call her Superteen as the episode ends.
- Narrator: "A reactor, critical mass. The League, critical mulch.
- When the Mayor is on the phone, he orders several items from Smarter Image, a parody of the store, Sharper Image.
- This episode marks the first appearance of Quarky the Lab Girl.