Mrs. frisby, the head of a family of field mice, lived in an underground house in the vegetable garden of a farmer , she was a widow , she has four children , their names are Martin, Teresa, Cynthia, and Timothy. 

Timothy was sick and he needs help, so mrs.frisby goes to search for mr. Ages , who she hopes can help her save Timothy. On her way to Mr. Ages' house , she heard a scream and sees a crow tied up to a fence post by his foot. She was scared but she goes to help him , and the crow said his name is Jeremy. and she told him about timothy sickness , and he told her to go to see the Owl , and Jeremy let mrs. frisby to hop on Jeremy's back and he'll take her to the owl .  After Mrs.frisby met the owl , he adviced her to "go to the rats."

Mrs. Frisby, still terrified, does what she is told and goes to visit the rats. At first, they won't let her in

they allowed to mrs.frisby to meet the rats inside the house . 

when she entered the house she met some rats and they became friends with her, and they told his husband die while he trying to put the powder in the food of the cat, she heard about there is a second chance for put the powder on food of cat again , she volunteered to put the powder . 

she is inside Mr.Fitzgibbon's house to put the powder , she goes to put it inside the food and she put it but when she wants return back , there is a boy was sitting on the table , he saw mrs.Frisby and he captured her and he put her in bird's cage . Mrs.Frisby heard woman said he will call scientists (NIMH) to come and kill all the rats in the farm by poison gas .

After while there is a rat called JUSTIN , he helped mrs.Frisby to open the cage and they ran away .

All the rats ran away from the house but there are 10 rats stayed to clean because they don't want the scientists know about the house , but the scientists killed 7 of them . Mrs. Frisby told to the rats to Transfer the house quickly before the scientists come .

After that Mrs.Frsiby came back to her children and she told them about their father's story and the Rats of NIMH .