Ralph the mouse lives with his family under the knothole in room 215 of the Mountain View Inn. His days at the run down motel in the Sierra Nevada of California are boring and he longs for a life of adventure. Things begin to look up when a boy named Keith and his family comes to stay in room 215. Ralph quickly notices that Keith has a shiny toy motorcycle, and he knows that he is destined to ride it.
Ralph can’t contain his curiosity. Ignoring his mother’s warnings, he scurries up a telephone cord to get a closer look. To his dismay, he cannot figure out how to get the motorcycle to run. The phone rings and startles Ralph. He falls into a wastebasket with his beloved motorcycle.
Soon enough, Keith discovers his missing motorcycle, along with Ralph, in the wastebasket. The mouse and child speak the same language, and quickly become fond of each other. Keith teaches Ralph that he only has to make an engine noise “pb-b-b-b” to make the motorcycle run. Although Ralph’s mother worries about him talking to humans, Keith lets Ralph ride the motorcycle to his heart's content, though only at night, so no one will see him. One night, Keith’s mother, who is terrified of mice, spots Ralph and reports the sighting to management. Ralph’s family is in danger, as the hotel begins looking more closely for mice.
Unable to resist riding the motorcycle during the daytime, Ralph almost gets sucked up by a maid’s vacuum cleaner, and barely escapes – riding the motorcycle into a pile of dirty linens. He has to chew his way out, and can’t manage to save himself and the motorcycle. Feeling guilty and irresponsible, he returns to his mouse hole – too ashamed to face Keith.
Keith forgives Ralph for losing his motorcycle, but loses trust in him. He continues to bring room service to the colony of mice, who are laying low after management discovered the chewed through sheets. One night, Keith becomes very ill with a fever, and Ralph is determined to regain his trust! Ignoring his family’s warnings, he sets off to search the hotel for an aspirin tablet. His mission becomes a dangerous one – he gets stuck under a glass cup, ventures outside the hotel where owls could easily eat him, gets chased by a dog, and finally comes up with a plan to bring Keith’s toy ambulance down to the first floor to retrieve the aspirin.
When Ralph succeeds in bringing Keith the aspirin, he redeems himself, restoring Keith’s health, and the boy's trust in him. Keith’s vacation is nearing an end, but he agrees to let Ralph keep his motorcycle, which is found by the kind bellboy. After Keith leaves, Ralph uses the space under the TV set as a garage, and the motorcycle is his to keep!