I understand, missing the killer pretty much killed the campaign. In the story, now that the killer frightened the town it will try its maximum to make them leave, meaning everyone who stays in town will be murdered until the town is empty. As you mostly guessed it is a druid who turned entirely against civilization, and want to get rid of any town where she leaves.
If you have some questions about the story, I can answer them before you leave.
I will close this campaign after.