Zira is an alien girl who finally gets her own little earthling, Rolo. His childhood as a pet is filled with play, treats, and naps. But as he grows older, the routine life becomes dull, and Zira doesn’t understand his desire for more independence. After encountering alien protestors for earthling rights, Rolo starts wondering where earthlings came from and how they lived before they were pets, but that ancient history is mysteriously missing.

While at an earthling park, the overzealous robots of the Animal Control Force (earthling catchers) chase Rolo because his pet license is expired. He and his best friend run away and get lost in the city. Now off leash for the first time, he goes on a quest to learn about the mythical planet Earth. He discovers clues from a pet store, a museum, and an old alien star captain, and he meets a stray street earthling living a life of freedom.

Meanwhile, Zira and her sulky older sister search for Rolo, arguing often while still coping with the loss of their big brother. When they finally find Rolo, he tells Zira he wants to be more than a pet and go find the fabled planet Earth, but she cannot bear to lose him too. Soon the earthling catchers close in, and they must escape to go home, wherever that may be.