Having vowed revenge on her for all the injustices placed upon them, Dr. Wakeman's mutant lab rats, led by the evil genius Vladimir, also known as Mr. Scruffles, plan to destroy her by taking control of Jenny's body.

On her first day of high school, Jenny seeks to make some new friends, and she thinks she can find some in the arrogant Brit and Tiff Crust. Unfortunately, the Crust cousins do not share the same feelings and plan to humiliate her.

When Jenny saves local school geek Sheldon from a gang of bullies, he quickly becomes smitten with her and does not want to leave her alone.

A simple snowball battle between Jenny, Brad, and Tuck is interrupted by a strange robot ambassador who wants to make Jenny the newest member of the Cluster, a legion of robots headquartered on the planet Cluster Prime that plans to enslave humans for manual labor. When she refuses, the ambassador commences war against her.

Jenny wants to get ear piercings, but her mother refuses to give her ears. Sheldon offers to step in and help, but the ears he builds end up being disproportionately large on Jenny's head.

Jenny and Brad's secret party is a hit, but between keeping the party-goers under control, keeping the house in one piece, and keeping a group of tiny multiplying aliens from invading Earth, Jenny has her hands full.

While on a mission in Japan, Jenny winds up losing one of her language system discs for English speech. Unable to switch off from speaking in full Japanese, she encounters problems in speaking to people. She uses this to her advantage, however, to make peace with a Japanese creature that grows with and is hurt by water.

Jenny has been invited to her handsome classmate Don Prima's latest party, and she has gotten a tune-up and a new paint job just for the occasion. However, Brit and Tiff are ready to do anything to sabotage Jenny's chances to impress at the party.

When Jenny finds and reactivates her "sisters"–early XJ prototypes 1 through 8–she is beyond happy. Each sister has her own personality, however, and they do not all have the same level of friendliness that Jenny has.

Jenny becomes the star football player of the high school football team. At a championship game, she soon finds herself facing the former Tremorton High quarterback whom she replaced.

When Jenny hangs up on Dr. Wakeman one too many times, the doctor desperately reprograms Jenny's communicator to make Jenny unable to turn it off.