Ralph S. Mouse
Beverly Cleary
 Ralph has befriended a young boy named Ryan, the son of the inn's new maid. Ryan has given Ralph the full name of "Ralph S. Mouse," the middle initial standing for "Smart." (The name is not seen in the previous two books.) Meanwhile, Ralph becomes agitated at his family. Forced by his parents to let numerous younger siblings and cousins ride his motorcycle, which is beginning to wear out due to their careless treatment and also worried that their droppings on the floor will result in anti-mouse retaliation by the hotel staff, he asks Ryan to take him to school, where he plans to hide and live out the rest of his life. Ralph is discovered by Ryan's classmates, who adopt him as a class pet and decide to see how smart he is by building a maze for him to run through. All this time Ryan is having difficulties with an aggressive boy named Brad from his class. Brad accidentally breaks Ralph's motorcycle, and Ralph blames Ryan and runs away to hide in the school. However, Ralph also confronts Brad for breaking his motorcycle, and Brad, realizing that Ralph can talk, offers to set things right for him and Ryan. Ryan and Brad discover that they have much in common and become friends. Ryan reclaims Ralph and brings him home on the school bus on the day that his new friend comes with him to visit at the inn. Brad also atones for his destruction of Ralph's treasured motorcycle by giving him his toy car. Ralph discovers that like the motorcycle, he can move the car by making car engine noises as a boy would do while playing with it. Ralph further discovers that he can safely give his younger relatives rides in the car without worrying that they will be irresponsible with it (but only Ralph can drive the car). Brad's father meets Ryan's mother and they marry six months later, thus Ryan and Brad are now brothers.