Prompt from goodpenmanship: an unused pistol.
"Watson, you brought your revolver?" Holmes whispered to me as we watched Harringer slip quietly out of the house.
"Of course, Holmes."
"Miss Dunloch, thank you for your assistance. Please, return to the house; the next part will be far too dangerous."
Miss Dunloch was clearly not pleased, but departed.
We continued to shadow Harringer, following him around the house to the large barn in the northern field. He went inside, and I drew my revolver, ready for the confrontation.
A sudden shout split the night. "Scotty!"
It was Miss Dunloch.
Rushing forward, we slammed open the barn door to find Miss Dunloch had beaten us to our quarry. She stood over him, a pitchfork in her hands, while he cowered below her. "Elsie, please! I had to do it! It was too easy - I would have shared the money! Elsie!"
Holmes recovered his equanimity admirably. "Thank you, Miss Dunloch. Would you be so kind as let me tie up our dear friend Mr Harringer?"
"Of course, Mr Holmes." Miss Dunloch stepped back, straightening her skirts and regaining her image as a prim and proper young lady - until she pulled a pistol out from beneath her skirts. "I knew Scotty was a coward. I didn't even need to use this!"