Marion Mill has had her fair share of clashes with her archenemy, Penny Park. After all, Penny is in the A-list girl clique, and Marion is a goody-two-shoes bookworm. However, after a mysterious transformation takes place between the two of them, they enter a whole different world—the world of each other. They soon realize if they want to get out of the predicament they’re in and return to their normal selves, they will have to work together and learn to respect each other. Will Marion be able to survive the pressures of ballet, a mansion of a house, and a mysterious blue-eyed boy? Can Penny withstand the demands of playing hockey, smelling like a horse, and attending algebra class? As they go through the journey of being one another, they realize that there are more important things in life than money, fashion, daily hygiene, and themselves. Can they unravel the mystery that caused their transformation? Or will they forever be Inside Out?