Ralph S. Mouse is the third in a children's novel trilogy that was written by Beverly Cleary. It features Ralph, a mouse with the ability to speak, but only with certain people who tend to be loners. It was first published in 1982, illustrated by Paul O. Zelinsky.^[1]

A film adaptation was broadcast in the ABC Weekend Special series in 1991.

Ralph, now an adult, still lives at the Mountain View Inn, a fading ski resort near Cucaracha, California. Ralph spends his days hiding under the grandfather clock and waiting for nighttime, when he can don his red helmet and race through the halls on his tiny red motorcycle. However, these days Ralph's motorcycle is showing signs of overuse. His relatives always beg him to give them rides on his motorcycle, but their constant demands are wearing both his tires and his nerves thin.

Ralph has befriended a young boy named Ryan, the son of the inn's new housekeeper, Mrs. Bramble. As they watch a car stunt show, Ryan says he has a classmate named Brad who races motorcycles, and Ralph thinks he might like to meet him. Matt, the inn's custodian, can also communicate with Ralph, and he helps him and his other indoor relatives evade the eye of the inn's prickly owner, Mr. Minch. One night after a snowstorm, guests arrive and leave melted snow puddles in the lobby. Ralph races through them, excited by the crests of water, but his relatives soon overtake him and beg for rides. Matt helps shoo away the throng, but they leave behind their droppings. The next morning, Mr. Minch scolds Matt for not doing his job and threatens to fire him if he doesn't eradicate the inn of all mice. Ralph feels terrible for causing Matt stress and feels he must leave the inn. If he leaves, then his relatives likely won't come out each night and make a mess. Ralph begs Ryan to take him and his motorcycle to school and hitches a ride in Ryan's pocket. When they arrive, he realizes that it may not be the haven he imagined.

Ryan presents Ralph to his classmates, and his teacher, Miss K, suggests that the class will research mice and conduct a Mice Exhibit, which will conclude with Ralph running a maze to demonstrate his intelligence. Ralph despises being put on display and feels very anxious about running the maze. He begs Ryan to help him, but Ryan wants his classmates to be impressed by what his pet mouse can do, so he tells Ralph he can't leave and can't have his motorcycle until he runs the maze. Ralph, angry, demands to return the motorcycle, but Ryan refuses and leaves Ralph alone at school overnight. Ralph scavenges the classrooms for food and shelter and collapses each night with exhaustion.

The mouse exhibit day arrives, and the anticipation fills Ralph with anxiety. A reporter from the local newspaper arrives to photograph the students and report on the exhibit. The students display art depicting Ralph and recite poems about mice. Gordon delivers an informational presentation on all the negative characteristics of mice. The time for the grand finale arrives, and Ralph trembles with fear as Ryan places him in the maze. Ralph is so overstimulated he can't detect the scent of the peanut butter and struggles in the maze. Using his creativity, Ralph scales the wall and easily traverses the top of the maze to the end reward. Brad claims Ralph cheated and Ryan forces him to run the maze again, but Ralph repeats the maneuver. Brad and Ryan begin arguing, which escalates into a fight. After Miss K defuses the conflict, Ryan realizes that Ralph's motorcycle was destroyed in the tussle. Ralph is overcome with sadness, and he feels betrayed by Ryan.

When the students return to school the following Monday, they bring the latest edition of the newspaper, which features the reporter's story on the exhibit. Instead of highlighting the students' hard work, the reporter insinuates that the school is overrun with mice and suggests that the school board take drastic extermination measures. Angry at being misrepresented, the students ask to write complaint letters to the newspaper. They also worry that Ralph will be caught in one of the traps set by the school officials. Miss K speaks with the principal, and he assures her that they are only setting a few traps. The next day, when no additional mice are captured, Miss K allows the students to write their letters. Miss K forces Ryan and Brad to apologize to one another for the fight, but they still argue over who's at fault for breaking the motorcycle. Brad thinks Ryan's family has the means to replace it since he lives in a hotel, but Ryan explains that he only lives there because his mother is an employee. Brad's tone changes and the boys' relationship begins to grow.

Ralph decides to speak to Brad and reprimands him for breaking his motorcycle. Enchanted by the talking mouse, Brad asks if they can be friends, but Ralph demurs. Ralph attempts to hide from everyone, including Ryan, but Ryan captures him and promises to return him to the inn. Ralph doesn't know how he will face his relatives without his trusty motorcycle. Brad accompanies Ryan home on the bus, and the two boys learn that they each hold unfair assumptions about one another. Brad's parents are divorced, and he lives with his father. Ryan doesn't know where his father is and admits that sometimes it's hard living in a hotel. When they arrive in the lobby, Brad gifts Ralph a tiny sportscar. Amazed at his new hot rod, Ralph slides in the seat and tries to start it with the same sound he used for the motorcycle, but it doesn't work. Brad tells him to try again, and soon Ralph is racing through the halls. Ryan reads the newspaper and sees that in response to the class's letters, the reporter printed a retraction to the mouse infestation story. Ralph's relatives then show up, eager for a ride in his new car. Ralph uses the skills he learned at school from Miss K to teach the mice to form an orderly line. Ralph reflects on all he endured at school but decides it was worth it if Ryan made a new friend and he learned to better communicate with his relatives. Eventually, Ryan's mother and Brad's father meet, marry, and move to a new home. Since Brad has a dog named Arfy, Ralph remains at the inn, safely tucked away under the grandfather clock during the day and racing his car at night.

• The Mouse and the Motorcycle (1965)
• Runaway Ralph (1970)
• Ralph S. Mouse (1982)

Churchill Films produced an adaptation of Ralph S. Mouse in 1990, directed by Thomas G. Smith, and animation directed by John Clark Matthews, starring Robert Oliveri as Ryan. It was produced by George McQuilkin.^[2] It aired as part of the ABC Weekend Special in 1991.^[3]