The rats and mice return to Thorn Valley to groom their destined leader, young Timmy Brisby.
Timothy Brisby, now Timmy, leaves his family to train with the rats of NIMH in Thorn Valley. He meets Jenny, a mouse about the same age as he, who reveals her family are part of "The Lost Six" who did not escape NIMH. Timmy suspects his missing brother is also being held at NIMH and embarks on a rescue mission with Jenny while encountering old and new friends along the way.
When Timmy is taken away to Thorn Valley, he is treated like a slave. Then, after finding a girl mouse, a mouse who's parents are captured, they set off to find the great owl. Little do they know they will run into trouble in this family movie.—Cheatmaster2006@hotmail.com