On the bustling streets of New York City, specifically on Fifth Avenue, known as the “richest avenue in the world,” a tour bus narrator draws attention to the dilapidated townhouse of Michael O'Connor, the world's second wealthiest individual. Amidst this backdrop, a middle-aged drifter named Aloysious T. McKeever, or “Mac,” accompanied by his loyal dog Sam, stealthily enters the O'Connor residence through a loose board and a manhole cover, seeking shelter for the night.
Meanwhile, O'Connor finds himself in the midst of evicting tenants from another one of his properties to make way for an ambitious eighty-story building. Among the displaced is Jim Bullock, a down-and-out veteran struggling to find work, who adamantly resists leaving. After an unfortunate encounter that leads to him being thrown out, Jim, while resting on a park bench, crosses paths with Mac. Seeing an opportunity, Mac invites Jim to come stay with him at the O'Connor estate, which he has unofficially inhabited for three winters while O'Connor spends his time in Virginia.
As the plot unfolds, O'Connor is preoccupied with plans to purchase Camp Kilson, a deserted army facility, to establish a significant air cargo network. His situation turns more complicated when he learns that his daughter Trudy has run away from her finishing school. Upon her arrival at the townhouse, Jim mistakenly assumes Trudy is a thief but allows her to stay, unaware of her true identity. Strikingly, she quickly develops feelings for Jim, opting to keep her wealthy background hidden to ensure he loves her for who she truly is.
When the night patrol arrives for a routine check, Mac devises a plan for everyone to hide and ultimately reveals to both Jim and Trudy that he is merely an intruder. In a heartfelt twist, Jim encounters fellow veterans Hank and Whitey along with their families, who are living in their car due to post-war housing shortages. Inspired by Mac, the group begins to brainstorm renovations to repurpose vacant army barracks as housing solutions and sets their sights on bidding for Camp Kilson.
As the narrative continues, O'Connor returns to New York to find Trudy headed off to her new job at a local music shop. Although he insists she return to school, Trudy stands her ground, revealing she has felt isolated her entire life and desires to be with Jim. The situation thickens when O'Connor, intent on meeting Jim, agrees to disguise himself as a drifter. Much to everyone's surprise, Trudy persuades Mac to permit O'Connor to join their makeshift household.
However, O'Connor grows increasingly frustrated with his unexpected house guests, threatening to involve the police. To sway the situation, Trudy brings in her mother, Mary, who had left O'Connor years ago due to his workaholic tendencies. As sparks rekindle between Mary and O'Connor, Mac unwittingly encourages their reunion, believing they might marry. Problems arise when Mary learns of O'Connor's plans to undermine Jim by offering him a job far away in Bolivia. Fueled by exit anger, she decides to leave him, and with Trudy’s support, ultimately convinces O'Connor to allow Jim to purchase the property.
On New Year’s Eve, the impromptu family gathers to celebrate their upcoming contract as they prepare to part ways. Though Trudy and Jim, alongside Mary and O'Connor, extend an offer for Mac to stay, he assures them he has arrangements at O'Connor's estate in Virginia while bidding goodbye. In a heartfelt send-off, O'Connor promises Mary that come next November, Mac will find his way back through their front door.
