Secrets Hidden Under the Keys

Exploration Stage: Secret Room
From: Conductor
Description: I don't even want to think about why the "Order of Shadows" was bringing evil spirits into town! We have enough problems as it is. I was checking out the Chamber of Secrets and found a secret door in the wall. It definitely wasn't there before! Inside, there was a weird key stuck in the keyhole. Can you find it?
Completed: There's blood on this cursed key. And it won't come off! We're dealing with a very sinister killer, it seems. Did he keep his victims locked up somewhere?