On her way home from school Alex Mack is practically hit by a truck. The truck is carrying a top-secret chemical and spills it on Alex. Alex learns later that she has magical powers and shares this secret with her sister, Annie, and best friend, Raymond.

Alex asks her sister for help with a class science project, but ends up using her power to impress the teacher. This gets her into trouble when the teacher believes that the project was done by Annie, not Alex. Meanwhile, Dave and Vince disguise themselves as janitors in an attempt to find Alex.