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 and Raymond are continually harassed by upperclassmen Jessica and Ellen. One afternoon Jessica trips Alex in the school cafeteria as Alex carries a tray full of food. A food fight ensues and Vice Principal Heller assigns Alex, Raymond, Jessica and Ellen to clean up the cafeteria every afternoon. Both sets of friends blame each other for the trouble, and they agree to take up Raymond's challenge of two-on-two on the basketball court. The stakes: the losers have to admit responsibility to Heller and clean up the cafeteria by themselves.

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.

At career day at the plant, Alex is taped using her powers and she, Ray and Annie have to sneak back and get the tape.

The big dance is just around the corner and Alex still hasn't been asked by the only person she cares to go with. Everybody knows she dreams of going with Scott, but he's not the one hounding her for a date. Jerry, an obnoxious, insensitive and persistent ninth-grader is relentless in his pursuit of her. He won't take no for an answer, but Alex continues to put him off.

Annie's science project has been chosen as a finalist for the big science fair to be held at the Paradise Valley Chemical Plant. The whole Mack family is looking forward to spending Saturday at the science fair rooting Annie on, except Alex. Not only is she sick of witnessing Annie's triumphs, but the chemical plant is the worst place for her to be. It's crawling with plant spies who are constantly on the look out for "the kid."

Alex, Raymond, and Nicole are facing their first junior high school midterm in history class. Libby, the most popular girl in school, has her own ideas about surviving the midterm and studying isn't one of them. Libby decides to pull the fire alarm right before the exam.

Alex and Ray have a falling-out and Alex is afraid Ray will disclose her secret to the plant.

In anger, Alex jeopardizes her mom's job. Later, she tries to make it up to her.

A reporter from the Planet newspaper comes to the Macks' house to do a story; Alex's cold makes her powers go haywire.

Annie considers going away to school. Meanwhile, Alex's powers are going haywire and she must convince Annie not to go.

Alex and Dad have trouble connecting. They go on a day trip together and chaos ensues.