| Director | Gore Verbinski |
|---|---|
| Budget | $38 million |
| Box office | $125.4 million |
String magnate Rudolph Smuntz dies, bequeathing his financially cash-strapped factory and a dilapidated Victorian mansion to his sons Ernie and Lars. Following the will reading, both brothers suffer setbacks in their lives—Ernie, who shunned the family business to become a chef, accidentally loses his restaurant when a cockroach hidden in a box of cigars he inherited from his father's estate contaminates a meal he is serving to the mayor, causing the mayor to suffer a fatal heart attack, while Lars is thrown out by his greedy wife April, after he honored a promise to his late father to refuse letting a rival company, Zeppco International, buy the factory. Lars and Ernie reunite in a diner and learn of each other's misfortunes, leading them to spend the night in the mansion they inherited.
The brothers find themselves unable to sleep because of a mouse making noise, but in trying to catch him, they discover blueprints of the property. Through these, they discover the mansion was built in 1876 and is a fabled missing design by the architect Charles Lyle LaRue and would be worth a fortune if restored. Alexander Falko, a wealthy collector of LaRue artifacts, offers to buy the mansion, but they decide to auction the mansion, thinking it would be more profitable. Later that night, Ernie spots the mouse and informs Lars they must get rid of him, fearing a repeat of the cockroach incident. Several attempts are made, but the mouse, proving to be remarkably intelligent, manages to outwit them every time.
Their situation becomes further complicated when Ernie borrows against the house to pay for renovations and the bank threatens to evict them in two days, unless they resume mortgage payments. After the factory workers go on strike upon learning they cannot be paid when Lars attempts to run operations on his own, Ernie goes behind his back to secretly meet the Zeppco representatives over their buyout offer upon finding the business card they left. The meeting fails to happen after he is hit by a bus while flirting with some women but is surprised when Lars reveals April will provide the cash, having learnt of the brothers' recent discovery. After more failed attempts to kill the mouse, including adopting a vicious cat named Catzilla and hiring an exterminator named Caesar, the brothers overhear a voicemail message from Zeppco withdrawing their offer, leading them to argue against each other. Their argument unwittingly leads to Lars throwing an orange at Ernie but instead hitting the mouse. Unable to finish it off, the brothers decide to mail him in a box to Cuba to be rid of it.
Ernie and Lars reconcile, and finish renovating the house for auction. However, on the night it is to begin, Lars discovers the box had been mailed back due to insufficient postage and realizes that the mouse is back in the house. As the auction gets underway, the brothers attempt to flush the mouse out with a garden hose but fail miserably when their actions cause the house to be flooded, washing everyone outside, before the mansion collapses. April leaves with a wealthy bidder, and the brothers, having lost everything again, spend the night in the factory. The mouse, surviving the collapse, follows them, whereupon it takes pity on their situation and uses the factory machinery to convert a block of cheese into a ball of string cheese. Inspired, the brothers end their war with the mouse, renovating the factory to produce string cheese, with Lars managing the business and Ernie managing the products. As a token of gratitude, they hire the little mouse to be their official taste tester and spokesperson.