Para Dexter, todo dia é um grande dia para a ciência! Dexter é um jovem gênio que planeja aventuras longe dos olhos atentos de seus pais. Ele somente é interrompido por sua irmã mais velha, Dee Dee.
In "Deedeemensional", Dee Dee time-travels to save Dexter from a monster. In "Magmanamus", Monkey goes up against a lava being that dislikes human-caused noise. In "Maternal Combat", when his mother falls, Dexter creates a robot mom to substitute for her.
When his mother falls ill, Dexter creates a robot to do her chores. Dee Dee gets hold of its remote control and wreaks havoc, forcing Dexter to create a second robot to counter Dee Dee's.
In need of an assistant to operate his latest invention, Dexter performs a brain transplant on Dee Dee to make her smart enough to fulfill the role. With her new brain, Dee Dee proves to be more intelligent than Dexter.
Mandark Astronomanov, a new student at Dexter's school, seems to be superior to Dexter academically. Mandark forces Dexter to shut down his lab so that Mandark's lab can gain more power. However, with the help of Dee Dee, Dexter manages to destroy Mandark's lab.
Banned from watching a late-night movie due to his young age, Dexter uses his technology to artificially grow into adulthood, but Dee Dee tampers with his machine, causing Dexter to turn into an old man.
Dee Dee and her friends, Lee Lee and Mee Mee, enter Dexter's lab and wreak havoc. Dexter clones himself to stop them, but the girls too make clones of themselves.