I admit, I have a big soft spot for animal fiction (specifically when the animal is the protagonist). I was introduced to the genre quite predictably by the Redwall series and as such I tend to consider the style/conventions of the Redwall series as the 'norm' for the genre. I was drawn to Thunder Oak because it starred weasels as good guys instead of villains (which is what they usually are). Since weasels are my favorite animal, well, this appealed to me. Needless to say, I had no idea what I was walking into.
Thunder Oak is the first book in the Welkin Weasels series. The plot is basically that humans mysteriously left the island of Welkin generations back and in that time the animals have become more human-like, taking on human values and such. Each species has its own unique customs and different extents to which they mirror humanity. Weasels and stoats are centered on in the story as weasels have essentially become oppressed by the more powerful stoats. A weasel named Sylver and his band of outlaws set out on a quest to find clues to find the humans and bring them back.
Pretty much all books with anthropomorphic characters are considered "Fantasy" but this is one of the first ones I've read that really takes advantage of that label. You go in expecting a sort of Robin Hood-esque story in a mirror of old England. Then you suddenly reach a paragraph that explains that in human's absense, statues have taken on life and wander the countryside. The world of Welkin is very magical, but not in the typical ways which makes it unpredictable and thus a great read. Highly recommended, especially for anyone who likes animal fiction.
Two words of warning - The books have unfortunately never been published in the US, so if you're American like me the book is a little more difficult to obtain and may be a little difficult to read at first since its written a wee bit differently than American books (all dialog is in 'single quotes' instead of "double quotes"). It isn't that hard to adjust to, though.
Secondly, its important to know that Thunder Oak does NOT answer all the mysteries it sets up - the next two books, Castle Storm and Windjammer Run, are directly connected and you need to read all three to finish the mystery of the missing humans and such.