The last we saw Charlie (Felicia Day) on Supernatural, she was high-tailing it out of town with a one-way bus ticket and a new crop of scarring memories thanks to helping the Winchesters take on Dick Roman.
The computer genius and all around Geek Girl extraordinaire proved to be of great help to Dean (Jensen Ackles) and Sam (Jared Padalecki) once before, when they needed someone with her expertise to hack Roman's computers. It has been over a year since the Winchesters have crossed paths with Charlie, but soon enough, they are going to need her particular brand of knowledge again when they stumble upon the death of a couple of LARPers. Wouldn't you know it? Charlie has extensive knowledge about that world-- and the particular game the two were playing when they were killed.
How have Dean and Sam survived without her!?