The heroes are sent to find what happened to a local druid, but discover his mind has been driven to madness and he is attacking the local villages. The heroes track down the druid's grove and find he was enchanted by a hag, and the heroes have to find a way to destroy the chimes she uses to enchant the druid.
"Karameikos Campaign Setting" doesn't appear to be a book, at least as far as I can google.