|Cameos|| Operation: Z.O.O. |
"Leaky" Leona is 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 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. Thus, they 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 school's underground area before finding Leona, who the effects of the fountain have worn off of, as 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 betrays the KND and shoots them with a water gun containing water from the fountain that regresses their age, turning them into babies.
Having 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. She started spraying the water onto all of Sector V, and despite the team trying to run for it, all five were turned back into babies. Numbuh 5 tries talking her out of it, but Leona didn't care although the Kids Next Door are saved by the Delightful Children's intervention, as they try to crush Leona and end up destroying the fountain. When the fountain is destroyed shortly after, Leona tries to jump into the chasm below to stay with her precious fountain, but is stopped. Afterward, Leona seemingly accepts that she can no longer be young, but at the end of the episode, happily for her, she finds a filthy drinking fountain in the hallway (which pipes presumably had access to the water of the fountain) which turned her into a kid yet again, but this time, she is able to go farther than the school grounds.
- In Operation: Z.O.O., when Numbuh 3 and 4 are setting the "Ugly Kids" free, one of the Kids looks like Leona. It's probably her, with different clothes.
- She was one of the kids who were delighfulized by the Delightful Children in Operation: D.A.T.E..
- Numbuh 3 thought Leaky Leona was the prettiest girl in the school until she saw her.
- Her name, Leona, is a reference to the legend of Ponce de Leon, a Spanish explorer who said to have discovered the legendary Fountain of Youth 400 years ago.