"I don't want to spoil anything but my character is set to cause some ructions. He definitely will shake things up. It's going to be fun. I started filming yesterday. When I stepped on to the set at Highclere (Castle, where the show is filmed), I thought, 'Yes, I'm home' - I'm upstairs, naturally!" British actor Richard E. Grant's guest character on U.K. period drama Downton Abbey is set to cause trouble.