Previous installments can be found here. There will be spoilers. “An historian” is a perfectly acceptable Commonwealth convention, haters to the left [side of the road]. A spectre is haunting Downton Abbey. It is the spectre of the Russian Revolution. In last week’s episode, Tom Branson described the Russian Revolution of 1917 as the only worthwhile thing to come out of World War I. This week, we learn that Rose is planning to become involved…