Harry Coombes (Art Carney) is an elderly widower and retired teacher who is forced from his Upper West Side apartment in New York City because his building is going to be razed to build a parking lot. He initially stays with his eldest son Burt’s family in the suburbs, but eventually chooses to travel cross country with his pet cat Tonto.
Initially planning to fly to Chicago, Harry has a problem with Airport Security checking his cat carrier. He instead boards a long-distance bus. He gets off in the countryside, annoying the driver, so Tonto can urinate, then buys a 1955 Chevrolet Bel Air from a used car salesman, although his driving license is expired. During his episodic journey, he befriends a Bible-quoting hitchhiker (Michael Butler) and underage runaway Ginger (Melanie Mayron), with whom he visits an old sweetheart (Geraldine Fitzgerald) in a retirement home, who only half-remembers him. He visits his daughter (Ellen Burstyn), a bookstore owner in Chicago, with whom he shares a prickly but mutually admiring relationship. Ginger and Harry’s shy grandson (who was supposed to bring him back to New York) end up going off to the commune in Colorado together in Harry’s car, with his blessing, so he and Tonto are on their own again.
Continuing west, Harry accepts a ride with a health-food salesman (Arthur Hunnicutt), makes the acquaintance of an attractive hooker (Barbara Rhoades) on his way to Las Vegas, then spends a night in jail with a friendly Native American (Chief Dan George). He eventually arrives in Los Angeles, where he stays with his youngest son (Larry Hagman), a financially strapped real-estate salesman, before finding a place of his own with Tonto.
After Tonto’s death, Harry is living alone, making new friends, enjoying the climate. As the film ends, he sees a young cat who looks exactly like Tonto, and follows him to the beach, where a child is building a sand castle.