On the picturesque Golden Pond, which is actually Squam Lake nestled in Holderness, New Hampshire, we find the elderly couple, Ethel and Norman, returning to their summer cottage. The moment Ethel steps inside, she is filled with joy as she hears the loons calling out to welcome them back, although Norman, reflecting the bittersweet changes of age, insists he hears nothing at all. They embark on the familiar task of uncovering the furniture and flinging open the windows, all while Norman's declining memory begins to hint at the subtle emergence of his senility.
Ethel, brimming with energy and clarity, playfully reassures him that they are merely in their late middle age since she is still in her 60s and he in his 70s. In contrast, Norman lets his mind wander towards thoughts of mortality; having retired from his career as a college professor many years prior, he can’t shake the sense of looming finality. The spirit of adventure is rekindled as they take a canoe ride on the water, thrilled to encounter loons. However, their serenity is abruptly shattered by a speeding boat that blares through the placid lake, igniting their ire as they retaliate with a few choice gestures and shouts. Later, as they fill up their motorboat with gas, Norman stands up to some teenagers who mock him for his age.
Ethel, vibrant and active, decides to send Norman off to gather strawberries from a nearby patch. Yet, during his stroll, he becomes confused and frightened, straying off the beaten path and into the woods. After an arduous sprint that leaves him breathless, he manages to find his way back to their cottage without letting Ethel in on the unsettling episode. Once settled, Norman attempts to distract himself by reading the baseball results in the newspaper, while Ethel reads aloud a letter from their daughter, Chelsea, who is set to visit soon with her new boyfriend, a dentist. Their conversation shifts to the local postman, who relays the news of a longtime resident’s passing at the grand age of 97, prompting Norman to question the fairness of life once more.
After the postman takes his leave, Norman reveals his disquietude to Ethel about losing his way, prompting her to embrace him and promise that they will walk together to help regain his memories. His insecurities surface as he wonders aloud why Ethel loves him so much. The day arrives for Chelsea's visit on Norman's 80th birthday, and as he puts on his tie, Ethel reminds him to be cordial to Chelsea and her boyfriend. The reunion is awkward as Chelsea greets him with an informal “Norman,” and he bluntly retorts with a remark about her weight. Soon, Chelsea introduces her boyfriend, Bill, along with his 13-year-old son, Billy Ray, which leads to a series of uncomfortable exchanges about aging and much-needed reconnections.
With Bill still reeling from a recent divorce, he struggles to articulate how Chelsea has positively impacted his life, adding to the disquiet as Norman sarcastically accepts Bill’s news about their shared sleeping arrangements. Meanwhile, Billy, with a penchant for the word "bullshit," reluctantly agrees to spend time with Norman, all while the adults engage in a skinny-dipping session in the pond under the cover of night. Later, Norman tries to bond with Billy, although their conversations play out awkwardly, with Norman suggesting Billy should read “Treasure Island” instead of bragging about his romantic exploits.
The dynamics of the family continue to unfold, with Chelsea expressing her anguish to Ethel about Norman's dismissive attitude towards her successes, despite her accomplishments in Los Angeles. Ethel implores Chelsea to confront her feelings from the past and encourages her to look towards the future. After Chelsea and Bill depart for a trip to Europe, Billy shares his contempt for his current situation, voicing a desire to venture westward alone. However, Norman wisely steers him toward a more sensible plan of fishing with him and Ethel, and the three of them set off on the motorboat.
As they enjoy a day out on the lake, Norman shares tales of a legendary trout he has unsuccessfully pursued for years, affectionately named Walter. Ethel eventually joins them, surprising them with a picnic lunch. The excitement of fishing continues as Norman when he manages to catch a large trout, albeit not Walter, culminating in joyful shouts over a minor victory.
Yet, their serene summer is not without mishaps. One evening, a fire that Norman starts in the fireplace spirals out of control, necessitating quick action from Ethel and Billy to extinguish it. Despite knowing that the incident was a result of his own carelessness, Norman’s frustration bleeds into his interactions with Billy. Ethel gently advises Billy to practice patience with Norman, who is trying his utmost to cope.
As time goes on, Ethel encourages Norman to allow Billy to take the motorboat out on his own, leading to unexpected tender moments. The sparks of camaraderie ignite as Norman shares fishing expertise with Billy, even when faced with unexpected challenges, such as a minor boat crash that sends Norman tumbling into the lake, only to be saved by Billy's quick thinking.
As the summer unfolds, a week passes with Norman and Billy recovering indoors. Once again, they set out for fishing after Ethel’s gentle prodding. Chelsea makes her return and is taken aback by the bond formed between her father and Billy. She candidly expresses her feelings of inadequacy and disappointment concerning her father-daughter relationship. Chelsea finally realizes the importance of reconciliation and acknowledges that she desires a better relationship with Norman, openly communicating that she has married Bill, a revelation which stuns Norman, but ultimately brings joy.
The climax of the summer reaches new heights as Billy catches legendary Walter, much to Norman’s delight. Chelsea watches the scene unfold, and Norman’s pride shines as he equals her happiness with open acceptance about her marriage. Their relationship blossoms further when Norman encourages Chelsea to attempt a dive off the dock, and she does so despite initial fear, showcasing the growth and trust between them.
As the day of departure draws near, Norman gifts Billy a prized fishing rod and offers Chelsea a long-held swimming medal he won in college, symbolizing the rekindled connection and love in the family. Their heartfelt goodbye leaves lingerings of newfound understanding, as Chelsea embraces her father, referring to him simply as "Dad" for the first time.
However, as the summer comes to a close, Norman's health falters; after lifting a heavy box, he collapses. In a moment of panic and fear, Ethel rushes to assist him. After an intense moment fraught with worry, Norman reassures her that the pain has passed. As they stand together, he catches the familiar call of the loons outside, signifying change and closure, leaving them to reflect on their life experiences, not unlike the loons, two souls who have perhaps watched their young ones leave the nest.
