A widowed field mouse (voiced by the late Elizabeth Hartman) has a sick child (voiced by Ian Fried) and two other children. They live in the garden of a farm where other animals live and feed.
They all need to move when it comes time for the farmer (voiced by Tom Hatten) begins to plow the field to prepare it for gardening. However, due to the sick child, "Mrs. Brisby" (Hartman) is reluctant to move.
She, with the help of of bumbling crow (voiced by the late Dom DeLuise), she seeks out the advice of a mysterious, but wise old owl (voiced by the late John Carradine). The "Great Owl" tells her to seek the assistance of the rats.
When she finds the rats, she is amazed at what she sees. They have the ability to use electricity, stolen from the farm, which a kind rat named "Justin" (voiced by Peter Strauss) frowns upon since stealing is wrong.
She learns of the rats story, where they lived at a place called N.I.M.H., or "NIMH" (which is short for the National Institute of Mental Health, a real-life medical organization in the United States), and gained an encreased mental ability thanks to experiments performed on them. She also learned that her late husband had his hand in the rats, and other animals, escape from NIMH.
The animation is real good in this movie, and holds up almost 30 years later. Though the majority of coloring is darker colors, the scenery and characters are animated fantasticly. Lighter hues are scarce in this film. The darker hues are best used with the "Great Owl", whose shot mostly in shadows so that his orange-yellow-tinted eyes stand out.
The characters are inhanced by the performers. Hartman made "Mrs. Brisby" kindhearted while in desperate need of saving her children. DeLuise made the crow a bumbling idiot, and was simply fantastic as the comedy relief.
Even though the parts were probably recorded separately, the on-screen chemistry is really good in this movie. Sometimes, you forgot you were watching an animated movie depending on who was on screen with whom.
The only major downfall of this movie is that the subplots of this film completely miss the mark. It is told in the movie that NIMH is interested in the rat population of the farm, but they are never seen on-screen as villains trying to recapture the rats. And the lead rat villain's (voiced by the late Paul Shenar) story of trying to take over the colony is completely relegated to a such a minor subplot, it's not even worth it. Personally, I would have tried to see the villain trying to create a stir by talking to others in the rat colony to envoke an uprising at just the right moment.
Character development is fairly weak in this film. Although there is some pretty good development in the main characters, the supporting characters are a miss. I didn't understand what many of the minor characters had to do with the plot, as they were really under developed. I really couldn't tell who was needed for more than just plot advancement, and who was not needed.
The music is pretty boring. I didn't even think it helped enhanse the action of the scenes. I remember at the end, just as the credits begin, there is one song with lyrics. This song would never be a Top 10 smash, or a Hollywood classic. In fact, it's pretty forgettable.
There is some mild violence, and one bad word in the entire movie. I might keep the Sesame Street crowd away from this movie because of these, and that the movie is not anything like a Disney movie.
I can just barely recommend this movie. It's almost a couple of notches above being skipable. Personally, I would check it on Hulu if there is nothing else to do.