So every once a while, there's a story you really, really want to do. I have one coming up next month: I'm covering the Agatha Christie Festival in Torquay, England. The festival is held every year, but this year is a big one, as it's the 120th anniversary of Dame Agatha's birth. As a dedicated fan, I've read all the books, seen all the films and BBC programs. And now I'll get to visit Christie's home, see her manuscripts, typewriters, memorabilia--and the garden of poisonous plants used to…