"Leaky" Leona was a strange and ugly girl at Gallagher Elementary School who years ago found an ancient underground school beneath the girls' bathroom containing the Fountain of Youth. However, since the water's effects are temporary, Leona was forced to live at the school and remain in the fourth grade forever in order to sustain her eternal youth. When the The Delightful Children From Down The Lane found out about the fountain, they determined to destroy it, not wanting anyone to be able to stay a child forever, kidnapped Leona and ordered her to bring them to it.

Upon hearing this, the members of Sector V leap into action to rescue Leona, discovering and traversing the underground school before finding Leona, who the effects of the fountain have worn off of, making her an old woman, tied up near the fountain. Sector V unties her and throw her into the fountain, thus making her a kid again - it is here that she explains how she is 300 years old and was able to maintain her youth via the fountain, but had tried desperately to keep it hidden from other children.

She concluded that she was thankful for their help, but could not take the chance of anyone else find out, so she betrayed the KND and shoots them with a water gun containing water from the fountain, turning them into babies. Having obviously gone crazy in maintaining and protecting her secret over the years, Leona intends to shoot them again, not only killing them but making them cease to exist. Luckily, Numbuh 5 is able to convince Leona not to do this.

When the fountain is destroyed shortly after, Leona tries to jump into the chasm below to stay with her precious fountain, but is of course stopped. Afterward, Leona seemingly accepts that she can no longer be young, but at the end of the episode, she is seen drinking from a filthy drinking fountain in the hallway which turned her into a kid yet again, but this time, she is able to go farther than the school grounds.

Her new way to stay as a kid forever was by using the sap of The Tree of Life. The Teen Ninjas knew about the tree and kidnapped her to give it to them. Sector V succeeded in saving her but failed to get the tree since The Delightful Children From Down the Lane kept it for the fruit that grew on it to make the tastiest cake ever. After that Leona was never able to be young again.