Freddy doesn't show up until 70% of the book is over, so if you're hoping for a Freddy book, lower your expectations. The book is pretty good, though, and the central mystery was sufficiently cryptic to intrigue my seven year old.
Freginald starts the story as a boy named Louise who is teased for having a girl's name; woke modern readers might be driven to hysterical rage.
A few chapters deal with a farm full of animals who are unaware that the Civil War is over, and they claim to belong to the Confederacy. When they hear that some of the circus animals come from Africa, a farm animal remarks, "We used to have slaves that came from Africa, too." Slavery isn't presented as good or bad, just as something that happened once.
Also, getting your hair permed is a central plot point, so be prepared to explain what that is.