On her way home, Brisby befriends Jeremy, a clumsy but friendly crow, before they both narrowly escape from the Fitzgibbons' family cat, Dragon.

Jeremy takes her to meet the Great Owl, who tells her to visit a colony of rats that live beneath a rose bush on the farm and ask for the services of Nicodemus, their wise and mystical leader.

From Nicodemus, she learns that many years ago the rats, along with her husband and Ages, were part of a series of experiments at the National Institute of Mental Health (NIMH for short).

The experiments boosted their intelligence, as well as making them capable of speech, rationalization and abstract thought, thereby enabling them to escape, as well as extending their lifespans and slowing their aging processes.

To avoid being at the mercy of humankind again, the rats have settled on a decision for them to leave the farm and live independently in an area they refer to as Thorn Valley.

Only Brisby can do this, as the rats cannot fit through the hole leading into the house; Jonathan was killed by Dragon in a previous attempt, while Ages broke his leg in another.

While trapped in a birdcage, she overhears a telephone conversation between the Fitzgibbons' patriarch and the staff of NIMH and learns that the institute intends to exterminate the rats in the morning.

[10] While they were still working at Disney, they produced the 27-minute short film Banjo the Woodpile Cat (1979) as a side project to gain other production skills that the company and their animation program were not addressing.

Two months later, former Disney executive James L. Stewart, who now had started Aurora Productions, called Goldman and told him about Anderson's idea of making a film based on NIMH.

One of the earliest drafts of the film was written by Steven Barnes, who received a creative consultant credit in the final product and was closer to the original novel.

[14] The story would have focused more on the rats and their time at NIMH as it did in the book, which was reduced to a short flashback in later revisions to bring Mrs. Brisby and her plight into the forefront.

A revised synopsis dated July 2, 1980, by an unattributed author would take the film closer to its completed form, which ended with the mysterious disappearance of the rats, leading the characters and audience to wonder if they ever really existed, or were just an elaborate illusion.

The object was also meant to introduce a spiritual aspect to the plot, with the director remarking: "The stone or amulet is just a method of letting the audience know that Mrs. Brisby has found 'Courage of the Heart'.

Among other changes, the antagonist Jenner was given much more prominence in the film, being only mentioned in the book as a traitor who leaves, to "add drama" to the narrative by giving it a more visible enemy.

[13] Unlike the original work, Justin does not rescue Mrs. Brisby from the cage at the Fitzgibbons' house; instead, she helps her children without the rats' assistance by using the amulet, once again giving focus to her personal story.

[11] Elizabeth Hartman was cast as Mrs. Brisby, with Goldman calling her performance in A Patch of Blue "so believable and sincere that we all felt that she was right for the part".

[21] The Secret of NIMH: Original Motion Picture Soundtrack contains songs from the film written by Jerry Goldsmith and performed by the National Philharmonic Orchestra.

It was Goldsmith's first composition for an animated feature, which he admitted was such a departure from his normal work that in the end he approached the project like a live action score, employing the same kind of extended themes and structural development.

[22] Intrada Records issued a remastered limited edition album on CD on August 17, 2015, with one previously unreleased cue ("At Your Service", running 3:39) and three demos of "Flying Dreams" (as performed by Sally Stevens, Paul Williams and as a piano duet) totaling 10:09.

[25] Varese Sarabande did release the soundtrack on CD prior to the 1995 re-released reissue in 1986 with the artwork as the same as the LP jacket, but with a black background and a different track arrangement.

the Extra-Terrestrial (directed by future Bluth partner Steven Spielberg),[27] it performed better in those theaters alone in its opening week than Poltergeist, Rocky III, Firefox, and Star Trek II: The Wrath of Khan.

[28] NIMH grossed nearly $14.7 million in North America,[5] though it was more successful on home video, cable, and foreign releases, ultimately turning a profit.

[34] Don Bluth and Gary Goldman later oversaw a high-definition restoration of the film, which was released on June 19, 2007, in a 2-disc DVD set called the "Family Fun Edition".

The consensus states: "The Secret of NIMH seeks to resurrect the classical style of American animation and succeeds, telling a mature story with rapturous presentation.

Ebert found that NIMH may not resonate as well on an emotional level with younger viewers, since "it has so many characters and involves them in so many different problems that there's nobody for the kids in the audience to strongly identify with".

[41] Vincent Canby of The New York Times noted the film's animation was "something of a technical and stylistic triumph" comparable to that of Disney's golden age, but he expressed dismay at the narrative, finding it too complicated and lacking in an "easily identifiable central character".

[48] A direct-to-video sequel directed by Dick Sebast and produced by Metro-Goldwyn-Mayer Animation titled The Secret of NIMH 2: Timmy to the Rescue was released on December 22, 1998.

[49] Set several years after the events of the first film, the plot focuses on Mrs. Brisby's son Timothy as he struggles to live up to his father's prestigious reputation.

Apart from Dom DeLuise and Arthur Malet reprising their roles as Jeremy and Mr. Ages, respectively, none of the original voice cast returned for the film.

The film was to be produced by the team of Daniel Bobker and Ehren Kruger, with screenplay by Ice Age series writer Michael Berg.