A potentially dark fantasy novel set in Minnesota with magic monsters in it

Question

I remember reading this book when I was about 12 or 13, so it's a middle-school reading level and published around 2005 or earlier.

It's about a group of kids living in a wooded Minnesotan town who, after some set of events, find their world has magic monsters in it.

I tagged it as horror because I remember the book having darker tones when I was a kid. I'm also pretty sure the conventional fantasy creatures were a bit more twisted than their Harry Potter counterparts, and they were out to seriously hurt the kids in this book.

There also is/was an IRL insurance company named after the city in which the story is set.

Answer 1

It's a book series titled "The Grey Griffins" first published in 2006. The first novel was "Revenge of the Shadow King".

The Grey Griffins series follows the story of four sixth graders who live in the fictional city of Avalon, Minnesota. These four friends formed a secret order named The Order of the Grey Griffins, consisting of, Grayson Maximillian "Max" Sumner III (the leader) and his friends: Natalia Romanov (the marshal), Ernie Tweeny (the steward), and Harley Eisenstein (the warden). In The Revenge of the Shadow King, the Grey Griffins discover a link between their 'innocent' card game (Round Table) and a magic book (the Codex Spiritus) which Max discovers in his grandmother's attic.

So the town is fictional, however, there is a real life insurance company called "Avalon Insurance".