During his trip, Timothy meets Racso, the son of Jenner (a rat of NIMH introduced in first book who is widely considered to be a traitor).

Racso is also burdened by his family history, as his father deserted the rats' previous colony, placing them in danger of extinction.

One of the most anticipated events of the first book was the possibility of Mrs. Frisby's children (Teresa, Martin, Timothy, and Cynthia) having grown up to visit the rats themselves and partake in adventures of their own.

While it ties up this plot point cleanly, many readers criticized this, feeling that the other children had much potential and deserved more exploration.

In the end of the first book, it is revealed that NIMH had found a number of unusual rats dead, and it is assumed that this is Jenner's group.

Although he and the few surviving separatists had strong philosophical opposition toward the Thorn Valley group, they kept their distance, still believing that their way of life was better.