After you do the knot correctly, do below - with care about where the active spots are located.
Trap intruder:
Open the Count's cabin door. See the bald headed man with the eye patch. He throws a gold coin on the desk.
Look close at cabin door. Sylvie says the handle is different.
Use the Count's cane on the door handle.
Use the knot on the rope on the door handle.
The intruder is trapped. Go back to the police station.