Lars and Ernie Smuntz are brothers who inherit their father's dilapidated old mansion in a run-down neighborhood. Hoping to sell the property quickly and make a profit, the brothers are dismayed to discover that the house is essentially worthless due to its poor condition and the high cost of repairs. However, their fortunes change when they learn that the property has been recently appraised at millions of dollars due to its historical significance and the presence of a rare masterpiece by an obscure artist.
Despite their initial excitement, Lars and Ernie soon realize that they cannot sell the property until they evict the house's sole occupant, a tiny but incredibly tenacious mouse. The mouse is not only incredibly intelligent and resourceful but also extremely territorial, making the brothers' task of getting rid of it much more difficult than they had anticipated.
As they devise ever-more elaborate traps and schemes to capture the mouse, the brothers also face other challenges, including their strained relationship with one another and the interference of the unscrupulous exterminator they hire. The situation soon spirals out of control, threatening both the brothers' livelihood and their relationship with each other.
In the end, the brothers are forced to confront not only the mouse but also their own shortcomings and the true value of the house and their relationship with one another.