Tonight I ran a scenario called "Lost in a Book" from Arkham Now, which is one of the free PDFs I downloaded from GM Day. The plot, in brief, is that a very bad bibliophile who got hold of an Italian warlock's accursed text managed to transmute himself into the form of an evil magical journal, and was using anyone who read it to take brutal advantage of very young women. So, basically, Harry Potter and the Chamber of Secrets if Lord Voldemort was a serial rapist. My players had a lot of fun with it, even though the bad guy ended up winning in the end. I think they're really starting to warm up to mystery scenarios. It made me want to check out Arkham Now because it was so well written.
