The Pen refers to the pen that plays such a central role in the Bill Malloy's mysterious death storyline:
And I have to say that for me an appearance by THE Pen would be quite interesting.
And I'm very glad to see that it's leading in the poll.
Though, sadly, more than likely the "special guest" is a person. And as far as DS actors go, the most exciting would be to see someone like Henesy, Isles, or Kate Jackson - someone who's never been to a Fest. Almost anyone else will be a big
and a huge
.