A fieldmouse named Mrs. Brisby must move her family to a safe location before the farmer plows the field where they live, but her invalid son Timmy cannot go outside due to his pneumonia. She enlists the aid of some highly intelligent, escaped lab rats that have built a subterranean society inside a rose bush near the farmer’s garden. The rats, led by the wise Nicodemus, decide to help her physically move her house to repay a debt of gratitude to her late husband, who made possible the rats’ escape from the laboratory. But things become complicated when some of the rats decide to use the situation to kill Nicodemus and make it appear to be accidental.