I did have to put on sub-titles, the mumbling and the accent combined with very fast speech made it very difficult to follow in parts. And introducing new characters as well as characters we I had forgotten all about from the last series got me rather 
I thought it was Shirley Henderson (The Way We Live Now?, haven't seen Harry Potter) but she doesn't seem to age, so I wasn't sure. Gosh, I just looked her up and she'd 50!! She must keep a mirror in the attic.
As a detective I think Kevin Doyle would make a very good footman. However, his role may become significant unless the storyline is just a red herring.