The Perfect Poison - Amanda Quick
So far this is the Arcane Society novel that has stayed with me. I'm intrigued by the idea of sensing poison. Also, there's something so exotic about plant collections--hunting through the Amazon--even if it's not described in the book, the aura of adventure lingers. Plus there's Caleb -- I've been wondering what his story was.

---almost a Spoiler---

I thought the solution to Caleb's troubles was a little too pat. Didn't have to earn it at all.