Answer:
The book is about the conflict between man and nature. More specifically, the struggles of Mrs. Frisby vs. whether or not to face the plow head-on.
Explanation:
Frisby and the Rats of NIMH is Man (non-human protagonist ) vs. Nature. When Mrs. Frisby's son Timothy comes down with pneumonia, she faces a serious choice: try to escape to the woods to avoid plowing, or stay in hopes that their home will be missed by the plow.
