The story starts out with good conflict: Mrs. Frisby's son is sick but her cozy mouse house is in the way of the spring plowing. She goes to The Rats for help.
Things get a bit annoying when the story goes into flashback mode for a good share of the book. (The rats' backstory is fascinating and could easily have been the focus of the book, in my opinion.) However, it's a good opportunity to talk about flashbacks and story frames. There are a lot of fun "ah-ha moments" for the kids, and the rats' advanced civilization amazes me every time.
Mrs. Frisby and the Rats of Nimh won the Newberry Award in 1972. What a wonderful, timeless read by Robert C. O'Brien!