So are we now looking at a possible three murderers?
Owen from Corrie, who was the original bag on head murderer, as we discovered when he tried to do Lady Edith in.
The current string of similar bag on head murders, which are probably done by an unknown copycat who didn't realise s/he was supposed to sit really closely and watch the victims die. This person is also the person who ran over the internet girl, which I find odd because aren't murderers usually supposed to stick to the same methods in killing their victims?
And whoever killed Grace, who may or may not be Marcella / Grace's Mother's new husband who has a weird hobby of sniffing clothes.
Marcella better turn out to have murdered somebody for this to be worth it. I haven't taken to her, or to anyone else other than Lady Edith, so unless it ends with a mass murder of every single cast member except her and that other police woman with the hair (who could be the one to actually murder them all now I think of it), then Marcella being carted off for murder is the next best thing.