The Secret of NIMH takes the Newberry award winning book by Robert C. O'Brien and magically transforms it into a thrilling tale upon the big screen. This is the first film directed by celebrated animator Don Bluth and tells the tale of Mrs. Brisby, who is raising her children alone after her husband passed away. She is caring especially for her young son Timothy who is sick, when the first signs of spring start to show and her house is suddenly thrust into danger because the farmer will soon come to plow his crops. She learns that the only way to move her family and keep Timothy from danger is to have her entire house shifted to near a large rock in the middle of the field, an impossible task for a simple mouse, but not one that is above the talents of the rats of NIMH, who have gained a high level of intelligence and are able to use their brains to solve the riddle.
Using a system of pulleys they start to move Mrs. Brisbys cinder block home but one of the rats, Jenner, sabotages the effort in order to advance his desire for leadership. His treachery results in the death of the eldest of the rats of NIMN, Nicodemus, and faced with that evil, Justin confronts Jenner and defeats him in a battle of swords. With rain falling and making the already difficult task of moving the house into a near impossibility, a magical amulet saves the day and with the courage of a small mouse even against a tyrannical cat, the team is able to get her house to safety before the tractor comes and plows them over. As the film ends little Timothy is well on his way to a full recovery, the rats of NIMH have found a new leader in Justin, while mourning the loss of Nicodemus.