About The Secret of NIMH 2: Timmy to the Rescue
The prologue tells an abridged version of Nicodemus' tale from the first film. It also explains that Nicodemus prophesied that one of Jonathan's and Mrs. Brisby's sons would save Thorn Valley from NIMH (something that never happened in the first film). The youngest, Timothy, is chosen to go, much to the chagrin of his older brother Martin, who believes he should have been chosen. Martin decides to prove his quality, and goes off to find his own adventure. Timothy is taken to Thorn Valley and is tutored by Mr. Ages and Justin, but his brainstormed ideas are put into motion so fast that Timmy often forgets to think things through as he is too busy wanting to prove that he is a hero like his father. He also befriends Brutus.
One day he comes across a female mouse named Jenny, whose parents were two of the lost six mice who tried to escape NIMH but were thought to have died in the air shaft. It turns out they all survived and were recaptured by NIMH. Out of fear that something terrible is going to happen to them soon, she left to find help. She also says that she met Martin, who directed her to Thorn Valley. Timmy's mother reports that Martin has gone missing after one of his daily expeditions.