Timothy falls sick with a high fever and wheeze, and Mrs. Frisby decides she must get medicine from Mr. Ages.

Mr. Ages diagnoses Timothy with pneumonia and warns he must not be exposed to cold air for at least a month.

Mrs. Frisby frees Jeremy the crow from tangled string on a fence, and he promises to repay the favor someday.

Mr. Fitzgibbon starts his tractor and his sons announce that plowing the garden will begin in just five days.

Jeremy the crow flies Mrs. Frisby to the old owl's hollow in the forest at dusk to seek advice.

The old owl advises Mrs. Frisby to find the rats living in the rosebush and ask them to move her home.

Mrs. Frisby enters the rosebush and discovers the rats' underground civilization, complete with electricity, carpeted halls, and running water.

Nicodemus, the rat leader, greets Mrs. Frisby warmly and declares that Jonathan Frisby was a dear friend to all of them.

Nicodemus and engineer Arthur agree to move the Frisby cinder block safely to the sheltered side of a large stone.

Mrs. Frisby volunteers to put sleeping powder in Dragon's food bowl so the rats can work safely that night.

Mrs. Frisby sneaks through the farm kitchen and successfully slips sleeping powder into Dragon's food bowl.

Farm boy Billy Fitzgibbon traps Mrs. Frisby under a colander and locks her inside a bird cage.

Trapped in the bird cage, Mrs. Frisby overhears the Fitzgibbons say government inspectors are coming to gas the rosebush.

Justin the rat rescues Mrs. Frisby from the bird cage and she warns him about the arriving inspectors.

The rats successfully move the cinder block to safety, and the Fitzgibbon plow later passes it without damage.

Mrs. Frisby's youngest son Timothy falls dangerously ill with pneumonia just as the farmer prepares to plow the garden where the family lives. A medicine-maker named Mr. Ages gives Timothy a cure but warns he cannot be moved for at least a month, creating an impossible conflict with the fast-approaching plow. A chance meeting with a crow leads Mrs. Frisby to a wise old owl, who directs her to the mysterious rats in the rosebush, where she is welcomed as the widow of a beloved friend named Jonathan Frisby. The rats devise a plan to move her cinder block home to safety, requiring Mrs. Frisby to drug the farm cat Dragon — the very act that killed her husband. She is captured in the attempt, overhears that government investigators are on their way to destroy the colony, and must race to warn the rats before it is too late. The plan succeeds, the cinder block is moved to safety, and the plow passes harmlessly by.

Mrs. Frisby's desperate journey to save her family from the plow.

Mrs. Frisby finds an abandoned food cache inside a tree stump while searching for food on the first morning of spring.

On her way to Mr. Ages, Mrs. Frisby takes a longer route past the barn to avoid predators lurking near the forest.

A neighboring shrew warns Mrs. Frisby that the frost may melt very soon and recalls a year when the farmer plowed early.

Mrs. Frisby watches more than forty rats haul a length of electrical cable into the rosebush in broad daylight.

Jeremy tells Mrs. Frisby about the oldest and wisest owl in the forest and offers to fly her there that evening.

The owl refuses to help Mrs. Frisby at first but changes his mind when he hears she is Jonathan Frisby's widow.

Brutus, the massive rat guarding the rosebush entrance, blocks Mrs. Frisby's path and orders her to leave.

Mrs. Frisby finds Mr. Ages hobbling on a broken leg in the rat tunnel and he persuades Brutus to let her inside.

Justin escorts Mrs. Frisby through the rats' lighted underground hallways and down an elevator to the main colony chamber.

Young rat Isabella startles Mrs. Frisby in the library and reveals that NIMH is the place the rats originally came from.

Arthur the engineer assures Nicodemus that moving the Frisby cinder block is a quick and manageable job.

Justin shows Mrs. Frisby the enormous main hall where rats are building plows and stockpiling seeds destined for Thorn Valley.

Nicodemus announces that ten rats must volunteer to stay behind and distract the investigators while the others escape.

Brutus collapses unconscious outside the rosebush after an unseen rat shoves him clear of the gas-filled tunnel.

The Frisby family moves to their summer home by the brook and Timothy shows no trace of his former sickness.

Before Mrs. Frisby's crisis fully unfolds, small moments of luck and observation shape the story — from finding hidden food on a cold morning to watching rats haul wire in broad daylight. Her path toward help is built on chance encounters, including a warning from a neighbor about an early spring thaw and a crow's knowledge of the forest's wisest creature. When she reaches the rosebush, she must navigate a suspicious guard, a lucky encounter in a dark tunnel, and the remarkable underground world the rats have built for themselves. She tours a vast engineering operation designed to carry the colony toward a new and independent life in Thorn Valley. The story closes with the rats' narrow escape from the gas, the revival of one who nearly didn't make it, and the Frisby family's peaceful arrival at their summer home.

The hidden details of Mrs. Frisby's world and the rat colony she discovers.

Mrs. Frisby realizes that Timothy's need for warmth and the fast-approaching plow together create a seemingly unsolvable dilemma.

Mrs. Frisby discovers a blackboard in the rat library bearing the words 'THE PLAN OF THE RATS OF NIMH'.

Nicodemus explains how the rats were lured with food in a marketplace and captured by scientists using nets and flashing lights.

The captured rats are placed in individual cages in a white laboratory and injected with DNA designed to boost their intelligence.

The scientists run the rats through a maze designed to trick them into believing that completing it would lead to freedom.

Justin escapes his cage during the day and explores the laboratory, discovering the air ducts and gathering details for a future escape.

The scientists begin teaching the rats to read using pictures paired with letter sequences, not realizing the power they are granting.

Justin reads the printed instructions on his own cage door and opens it himself, proving that literacy is the key to freedom.

Jonathan Frisby and Mr. Ages squeeze through the air duct screen and unbolt it from the outside, freeing all the rats.

The rats spend a winter at an unoccupied estate, reading a vast library and each mastering a different field of knowledge.

The rats discover a dead toy tinker's truck full of small tools and mechanical parts and use it to build their colony.

Nicodemus explains to Mrs. Frisby how the rats' comfortable life of stealing under the rosebush trapped them in a pointless Rat Race.

Jenner refuses to accept Nicodemus's plan to move to Thorn Valley and leads several followers permanently out of the colony.

Jenner and his group are found dead at a hardware store, electrocuted while attempting to steal a motor.

Mrs. Frisby sits with her children at their summer home and tells them the full story of their father and the rats.

The roots of the story stretch back to a laboratory where ordinary rats were captured, caged, and transformed into beings of extraordinary intelligence — without ever being asked. The rats' journey from imprisoned test subjects to self-aware escapees is driven by a single crucial discovery: that literacy is the key to physical freedom, and it is a mouse named Jonathan Frisby who helps them take the final step out of the lab. After years of building a comfortable but hollow life by stealing from humans, the rats' leader Nicodemus identifies the trap they have unknowingly built for themselves and pushes for a bold new beginning in a hidden valley. The defection and eventual death of his closest friend Jenner forces the issue, drawing investigators to the farm and accelerating everything. The story ends with Mrs. Frisby passing the full truth about their father and the remarkable rats on to her children, ensuring the legacy of Jonathan Frisby endures.