Dexter is a bespectacled boy-genius who, behind a bookcase in his bedroom, conceals a secret laboratory, which can be accessed by spoken passwords or hidden switches on his bookshelf. Though highly intelligent, Dexter often fails to achieve his goals when he becomes overexcited and careless. Dexter conceals his lab from his clueless parents, addressed only as Mom and Dad who never take notice of it. His hyperactive, good-hearted, older sister Dee Dee delights in playing haphazardly in the lab, wreaking havoc with Dexter's inventions. Though seemingly dim-witted, Dee Dee, who is also a talented ballet dancer, can outsmart her brother and even give him helpful advice. For his part, Dexter, though annoyed by his intrusive sibling, feels a reluctant affection for her and will come to her defense if she is imperiled.