Robert, portrayed by Martin Landau, is a lonely elderly man who decides to wrap a single present for himself, placing it under his Christmas tree. Leaving his front door wide open, he heads to his job as a clerk in a grocery store. There, an elderly woman observes him from afar, while his eccentric boss, Mike, requests a meeting to discuss an idea about selling Christmas cookbooks.
Upon returning home, Robert discovers the woman from the store sitting in his living room, prompting an outburst as he angrily demands she leave. However, she quickly calms him, introducing herself as Mary, played by Ellen Burstyn. She explains her unexpected entry; she noticed his car had crashed into the garage and saw his door ajar.
Soon after, Mary visits again, asking Robert if they could have dinner together the following day. He agrees, relieved that she will drive since his recent accident has left him uneasy about driving. The anticipation for their date fills Robert with excitement, prompting him to clean up and seek advice from Mike and locals, although their suggestions often contradict each other. Meanwhile, Mary’s daughter, Alex, expresses her concerns about the implications of the date to her mother.
On the night of their dinner, Robert nervously offers awkward compliments on Mary’s appearance, as he had practiced. At the restaurant, they share their distaste for the food, revealing a mutual preference for TV dinners. They bond over their lives and experiences, promising one another that they would never give up hope. Their evening culminates in a magical carriage ride through the snow-covered town, where Mary confides that this is her first date since her husband's passing. Hesitantly, Robert puts off a kiss by drawing her attention to Christmas carolers. Before she leaves, he stammers that the date was wonderful, a sentiment she reciprocates by indicating she'd like to see him again.
The next morning, Robert wakes up filled with anticipation, eager to hear from Mary. His distraction leads him to buy numerous cheap sleds from kids selling them for charity. When Mary eventually arrives, they joyfully head out to sled, followed by a walk in the snow. During their stroll, Mary invites him to a Christmas Eve party, but Robert shares his feelings of having wasted his life, prompting her to reassure him otherwise.
As Christmas approaches, Robert counts down the days with excitement. He enlists Mike to help him pick a special present for Mary, and they enjoy a lively shopping spree. Afterward, Alex shares that Mary has genuine feelings for Robert, fueling his enthusiasm. In a pleasant turn of events, Mary proposes celebrating Christmas together, leading to a heartfelt kiss after he confesses he has never spent it with anyone before.
On Christmas Eve, Mary takes Robert to a festive gathering at her cousin’s house. Attempting to mingle, Robert finds himself in an awkward moment when a little girl greets him by name, only for her to burst into tears when he doesn’t recognize her. When Robert mistakenly confronts a man engaged in a conversation with Mary, suspecting him to be an ex-lover, she quickly sets the record straight, explaining he is merely a friend. The evening concludes as they share a slow dance in the softly falling snow, wrapped up in the magic of the moment.
Christmas morning brings joy for Robert as he wakes up to find Mary beside him. They eagerly exchange gifts, where he surprises her with a snow globe, and she gives him a paint set to encourage his artistic endeavors. The mood quickly shifts when Mary discovers a wrapped gift from Robert that contains a gun inside. He explains how his loneliness had driven him to the brink of despair, planning to end his life that day until he met her, which transformed his outlook. This outpouring of emotion leads him to declare his love for her, and they embrace tightly.
Later, Mike arrives to reveal that he has repaired Robert’s garage and brings Mary’s daughter, Alex, along. The four of them find comfort in sharing simple TV dinners together, creating a sense of family.
That night, as Robert and Mary settle down, he expresses that although their time together has been brief, it feels like she has been part of his life forever. With plans to propose, Robert is filled with hope. However, the next day, while painting, he temporarily loses sight of Mary, triggering a panic. Though she attempts to give him medication, he becomes confused and agitated, not recognizing her.
In a desperate attempt to find solace, Robert barricades himself in Mary's house across the street. Surrounded by images of a past life with her and their children, Mike and Alex, he succumbs to despair upon realizing he has lost precious memories of those he loves.
A poignant flashback reveals that Mary had prepared the house for Robert to maintain the illusion of a new romance, while their children had been helping her preserve his dignity and sanity. During a hospital visit, Mary brings Robert the snow globe he gifted her; however, he is now a shadow of his former self, offering little response. In a heartbreaking gesture, she promises her eternal love and lovingly places his wedding ring, which she had been wearing, back on his finger, signifying their unbreakable bond.
