Downton Abbey isn’t scared of killing off all of its major characters, that’s for sure. But after sending most of the main characters into the ground (literally), new characters have to be added to keep the drama up.
Luckily, Lily James, who appeared in the latter part of season 3 as the promiscuous, energetic Rose, has been promoted to series regular for season 4. There was really no question to her becoming a regular now that she will be joining everyone at Downton.
Rose will certainly be a fountain of drama and scandal for Downton; she is young and likes to party. She has a very liberal attitude and is the poster child of the post-war 1920s and everything that the era brings.