Alexandra (Alex) Mack lives with her prodigy older sister (Annie), her chemist father (George) and her business marketing mother (Barbara), in the modern corporate town of Paradise Valley. Located in Arizona, Paradise Valley has good weather but is incredibly small and has nothing exciting about it. Its main employer is the obscure and shady Paradise Valley Chemical Plant, where George works on various projects. Alex is thirteen and very concerned about her first day of junior high school.
She considers herself to be boring and average, and to have nothing special that stands out about her. She's constantly in the shadow of Annie, who has extreme talents in math and science, and she's embarrassed by her parents, who don't understand her feelings. Barbara packs Alex's lunch in a Trollz lunchbox on the first day of school, and Alex heads out with her best friend Raymond (Ray) Alverado, a kid who, like her, considers himself to be insignificant. Immediately things at school go bad for Alex - her class schedule is ripped in half by a fat boy stepping on it, she fails to answer properly in mathematics class and Ray abandons her to go join the band club. Alex is also bullied by an athletic girl named Jessica for her hideous lunchbox but Scott, a jock kid, intervenes. Dismayed at her bad day, Alex walks home solemnly, muttering to herself that she's a geek. Meanwhile Dave, a truck driver from the chemical plant, accidentally hits Alex with his truck, spilling a barrel of hazardous chemicals all over her. Terrified she runs home, only to find that she now has several powers (telekinesis, "zapping" and "morphing", in which she can turn into a clear gel-like puddle).
Annie and Ray keep it a secret, and Alex tries to live out her life as normal as possible, while doing her best to outwit Danielle Atron, the greedy and sadistic owner of the chemical plant and her security guard, Vince..