The Star Beast
Robert A. Heinlein
 An ancestor of John Thomas Stuart XI brought the alien, long-lived Lummox home from an interstellar voyage. The articulate, sentient pet he inherited has gradually grown from the size of a collie pup to a ridable behemoth—especially after consuming a used car. The childlike Lummox is perceived to be a neighborhood nuisance and, upon leaving the Stuart property one day, causes substantial property damage across the city of Westville. John's mother wants him to get rid of it, and a court orders it destroyed. Desperate to save his pet, John Thomas considers selling Lummox to a zoo. He rapidly changes his mind and runs away from home, riding into the nearby wilderness on Lummox's back. His girlfriend Betty Sorenson joins him and suggests bringing the beast back into town and hiding it in a neighbor's greenhouse. However, it isn't easy to conceal such a large creature. Eventually, the court tries to have Lummox destroyed, but is unable to do so, much to Lummox's amusement. Meanwhile, representatives of an advanced, powerful and previously unknown alien race appear and demand the return of their lost child...or else. A friendly alien diplomat of a third species intimates that the threat is not an empty one. Initially, no one associates Lummox with the newcomers, in part due to the size difference (Lummox was overfed). Lummox is identified as royalty, complicating the already-tense negotiations. It is discovered that, from her viewpoint, the young Lummox has been pursuing her only hobby and principal interest: the raising of John Thomases. She makes it clear that she intends to continue doing so. This gives the chief human negotiator the leverage he needs to avert the destruction of Earth. At the request of Lummox, the recently married John and Betty accompany her back to her people as members of the human diplomatic mission.