The story takes place on the planet Yietta, where the inhabitants generate income by exploiting the planet's one-of-a-kind liquid-gas oceans. Plastic Little commences as the Yietans prepare to finally pay off their debts to the Galactic Federation. However, some individuals are not willing to relinquish control over Yietta. Tita, the 17-year-old captain of the spaceship Cha Cha Maru, is introduced. Along with her team, Tita specializes in capturing Yietta's exotic creatures for interstellar pet shops, but due to unfortunate circumstances, she finds herself at the center of a scheme to seize control of the planet. Tita saves Elysse, a 16-year-old, from the military's grasp, endangering herself and her crew in the process. As the plotters gather their forces to capture Elysse, who they believe carries valuable computer code, Tita must engage in a perilous chase with a whole army of professional assassins. The situation is like a Cat and Mouse game on a planetwide scale, but with one critical distinction: mice don't shoot back, unlike Tita and her crew.