In a moment of transformation, Bart Hughes, a seemingly unremarkable investment banker by day, is thrust into a life-altering predicament. Having just turned down a family vacation in Vermont with his wife, Meg, and their young son, Peter, he soon learns that a crucial project meant to promote his career has been handed over to his colleague, James Hall. This setback is compounded by the added pressure from his boss, Eliot Riverton, who assigns him the daunting task of developing a comprehensive reorganization plan for the company's branch offices, all while racing against a tight two-week deadline.
As Bart attempts to navigate these challenges, he faces an even more pressing dilemma: a determined female rat has invaded his home. What first appears to be a minor inconvenience—an issue with the dishwasher leading to flooding—quickly spirals into chaos as Clete, the superintendent of a nearby apartment, exposes the substantial threat posed by the rodent. The seasoned tenant's insights force Bart to reckon with the unforgiving realities of urban wildlife.
With escalating tensions, Bart's often futile attempts to capture the rat only serve to aggravate the situation. His library research uncovers unsettling facts about rodents, which he inadvertently shares during a dinner party, leading to spoiled appetites and perplexed guests. As the days unfold, Bart becomes increasingly desperate, turning to a hardware store salesman for dire advice on pest control.
The rat's campaign of destruction escalates, culminating in a spine-chilling moment where Bart wakes to find the creature atop his toilet. This shocking encounter drives him to take extreme measures, culminating in a perilous showdown with the mother rat, transforming this ordinary conflict into a profound struggle for Bart’s identity, control, and the very essence of his life.
As the day at the office unfolds, Eliot acknowledges Bart's hard work but can't ignore the visible stress radiating from him. Bart insists that his troubles aren't work-related and anticipates they will soon pass. However, as the clock ticks towards five, he shares a taxi ride with his insightful secretary, Lorrie Wells, who hints at the underlying marital issues troubling him. Though Bart makes an attempt to connect further, Lorrie's attention is captured by the incessantly scurrying rat. In an effort to combat this unwelcome intruder, Bart decides to adopt a stray cat, only to be left devastated by its tragic demise shortly thereafter, symbolizing the unrelenting menace of the rat problem.
Bart’s struggles are compounded as he attempts—yet fails—to engage an exterminator, while his pleas for Meg to return from her vacation go unanswered. With tension mounting, he retreats into the darkness of his home, armed with a baseball bat, ultimately discovering that the report he had diligently prepared lies in ruins, chewed to shreds by the merciless rodent.
Emerging the following morning, disheveled and desperate, Bart confronts Eliot with the bittersweet revelation of his personal battles. In a moment of clarity amidst his turmoil, Eliot pragmatically advises Bart against exposing his colleagues to his current disarray.
Undergoing a chaotic evening, Bart injures himself while constructing a rattrap, leading him to seek refuge in a whiskey bath. Here, he drifts into a dreamlike state where the harsh realities are superseded by idyllic family reunions—only for this bliss to be shattered by the menacing pursuit of a rat that threatens his loved ones. Upon regaining consciousness, he finds himself in a life-or-death struggle with the wicked rodent, which now seems to embody all his fears.
As his friends attempt to reach him over the phone, thwarted by the rats that sever their connection, Bart prepares for a climactic confrontation. Donning protective gear fashioned from household items, he primes himself for a showdown unlike any other, unleashing his frustrations on the creature. The fierce skirmish causes chaos in his basement, culminating in the destruction of everything in sight. When the clash ends and Bart emerges from the wreckage, he is met with the concerned faces of Meg and Peter upon their return, prompting Meg to question the state of their home. Bart's flippant response, "I had a party," masks the hidden chaos of his reality, leaving the genuine strife of his struggle unspoken.
