When their string magnate father, Rudolf Smuntz, dies, brothers Ernie (Nathan Lane) and Lars (Lee Evans) move into his decrepit mansion. Struggling to keep a promise to never sell the now unprofitable string factory, the brothers decide that restoring the house, the last built by a famous architect, could bring them a great deal of money. But during their restoration attempts, Ernie and Lars are continually frustrated by a malicious mouse that keeps destroying their efforts.