As elderly residents navigate their daily lives in Manhattan, Harry, accompanied by his tabby cat Tonto on a leash, strolls along a sidewalk while reciting quotes from Shakespeare's King Lear. He makes a stop at the local grocer, where he buys some tasty treats for Tonto and humorously remarks that his days of romance are behind him. Later, he encounters his longtime friend Jacob on a nearby bench, sharing the news that his apartment is set to be demolished to make way for a parking lot. Jacob expresses his disdain for capitalists and reassures Harry that he can always move in with him if needed.
On his way home, a young thief attempts to snatch Harry's groceries and knocks him down in the process. Fortunately, he's aided by Leroy, the building superintendent. Once home, Harry converses with Tonto, expressing his frustrations over being mugged four times in just a year and mourning the declining state of the city he loves.
Days later, police arrive at his apartment to evict him and his belongings. Throughout this chaotic scene, Harry continues to quote King Lear, until his son Burt comes to collect him. Harry then relocates to the suburbs to live with Burt, his wife, and their two adult sons. The household is tense as Harry's younger grandson, Norman, has taken a vow of silence, causing friction between him and the rest of the family. Seeking understanding, Harry later inquires about books that explain Norman's beliefs.
Returning to his familiar bench to chat with Jacob, the two lament the long span since they’ve been intimate with anyone. Jacob fondly recalls his first sexual encounter with a servant at the age of 14. Harry eventually invites Leroy over for dinner at Burt's home. As Leroy plays the piano, Harry reminisces about life while Leroy shares that he lives with his elderly mother and struggles to find work, prompting Burt's wife to question why Harry hasn’t sought help from his other two children.
Feeling like a burden to Burt, Harry sets out to find his own apartment, but is disheartened to discover that the places he's interested in won't accommodate cats. He then tells Burt of his plans to visit Shirley, Burt's sister in Chicago, but before he leaves, he visits the morgue to identify Jacob's body, who passed away alone. Stricken with grief and memories of Jacob's life, Harry weeps.
At the airport, Harry learns he cannot carry Tonto through security and opts to take a cab to the bus station instead. During the bus journey, Harry asks the driver to stop so Tonto can relieve himself, but the cat takes off across a cemetery. Left behind by the bus, Harry scolds Tonto for his antics when he returns.
Determined to continue his journey, Harry buys an old Chevy for $250 and checks into a motel. A call to Burt reveals that his driver's license expired in 1958. As Harry drives through the countryside with Tonto perched on the dashboard, he reflects on his younger days when he dreamed of a road trip. He acknowledges his fear of pain, wishing for a quick death unlike the slow passing of his beloved wife, Annie.
On the road, Harry picks up two young hitchhikers—one soon finds another ride, while the second, a girl named Ginger, claims she's 16 and running away to a commune in Boulder. They share a motel room, and after she emerges from the bathroom in casual attire, Harry is reminded of his first love, Jessie, whom he hasn’t seen in 50 years. Ginger proposes that they try to locate Jessie, even if it takes them off course.
Eventually, they track down Jessie in a nursing home. Although Harry initially believes she remembers him, her senility causes confusion; she mistakes his name for Alex, yet still recalls Annie. At one moment, she even requests for Harry to dance with her, leaving Ginger watching affectionately.
Their journey leads them to Chicago, where Shirley owns a bookstore. To Harry's surprise, Norman is already there, sent by Burt to meet him. Norman has finally started to speak again, but the reunion is tainted by tension as Shirley mourns her fourth marriage. A conversation by the shores of Lake Michigan reveals Shirley's encouragement for Harry to return to teaching—a notion he dismisses due to his age.
Continuing their travels, Harry, Norman, and Ginger head towards Arizona. During this time, Harry calls Burt to explain his predicament, but it doesn’t go as planned. He and Ginger decide to part ways, leaving Harry with two seemly separate paths. He unexpectedly encounters a traveling salesman who sells him a blender he doesn’t need before hitchhiking again.
While hitchhiking, Harry is offered a ride by a striking redhead in a convertible, who turns out to be a high-priced escort. She playfully probes into his sexual history and, despite his initial hesitation, he discovers charm and allure in the prospect of closer companionship. However, when he admits to having just $100 to spare, she drives off after leading him up into the hills.
Left to his own devices, Harry finds himself at a Las Vegas casino. There, he enjoys a drink but soon draws the ire of another gambler who accuses him of ruining his winning streak. As Harry steps outside with Tonto for some milk, he is arrested while urinating against the wall.
Upon waking in jail, he meets Sam Two Feathers, a kind-hearted native Indian. In a moment of barter, Harry offers his new blender for the relief of pain in his shoulder, resulting in an exchange involving a pair of Harry's underwear.
After all the detours, Harry finally arrives in Los Angeles, walking along Hollywood Boulevard with Tonto until his son Eddie picks him up. Although Eddie initially presents himself as a successful real estate investor, he eventually confesses that he is broke. In a heartfelt moment, Harry reassures Eddie they will find a way to support each other, while providing a small loan to help him get back on his feet.
Spending time at the beach offers Harry a chance to relax, but his peace is short-lived when Tonto suddenly falls ill. Devastated, Harry takes his companion to an animal hospital, ultimately having to say goodbye to the cherished cat. Later, on the beach, as Harry pens a letter to Leroy about Tonto's passing, he encounters Celia, a woman accompanied by numerous cats. Flirting with Harry, she invites him to spend time with her, but he becomes distracted by the sight of a tabby that resembles Tonto.
Following the new cat onto the sand, Harry finds a little girl building a sandcastle against the backdrop of a serene sunset, reminding him that life, despite its challenges, can still hold moments of joy and connection.
