The Plot Mickens

"Well, well, Mydia," Marlene said. "What have we here?" She bent and picked up the folded paper.
"I saw what you did. I know who you are," the note read.
"How very unoriginal," Marlene said outloud. Mydia Meowed.
"Go to Northwest Wools tomorrow morning and ask for a package", the note continued.
That's better, Marlene thought. If you are going to threaten someone, you should at least be original.
Marlene was an avid knitter, but who would know that? Time to find out.
"Mydia," she said. "Hold my calls, I'm going to the yarn store."