Priory of Death: 17

"Outsider! This is where Connie died too..."
"Great! You found it!"
But that made no sense. What about the scream?
Of course! the killer wanted us to think she'd been killed outside, in the gardens. That was why we hadn't been able to find a muder weapon. Obviously Connie had gone here to test some theory about the pit, and the killer, suspecting that she had realised the truth, had murdered her. Then, to try and allay our suspicions (and I'm a suspicious kind of girl), the body had been moved out into the gardens. I'd surprised the killer while he or she was moving the corpse.
What truth had Connie discovered? Obviously she'd suspected either the motive for Mr. Hamilton's killing, or the method - both things that would point to one of our party. The answer had been down here. Here not only Connie Yorke, but James Hamilton, had died.
But why? The motive for Connie's murder was easy to understand - one the killer had begun to kill, he or she had to kill again to cover up the fact. But why would anyone want to murder Mr. Hamilton in the first place? Anti-religious fervour wasn't sufficient motive to set up a killing this complicated, and it didn't make sense anyhow. None of the guests were that way inclined. If Richard Dawkins had been invited I might have believed it, but this... But then, nothing made sense right now. This was a sealed room with the door closed...
Of course! I had a sudden flash of inspiration.
"Emily! Close the door!" I called.
"Grey..."
"Do it!"
"Okay!"
Emily slammed the heavy oak door. I looked around the walls of the 'pit'. They were all solid stone.
Then I heard the whirring of machinery. I felt the floor move beneath me, downwards like a lift. Looking up I saw the roof of the pit descending - set in motion by a switch operated by closing the door.

There was another door on a lower level! I saw it as the huge stone slab on which I stood descended. That accounted for the removal of the body, I thought. But surely there hadn't been that much time at the demonstration? And anyway, everyone had been there...
The descending ceiling, I thought. It had to be a replica of the floor I was standing on. We'd thought we were looking at the floor Hamilton had been tied to, but in fact we were looking at a completely different floor. It seemed excessively complicated...
No it wasn't, I realised with horror, as my torch picked out a patch of red on the descending ceiling above me. A patch that more or less corresponded to the one on the floor. Now I knew why I hadn't been able to find a murder weapon - it was far too big, I'd overlooked it.
And now I was standing right in it! A huge device for killing people.
"Emily!" I called. "Open the door!"
"I can't!" her voice came back. "It's locked itself!"
I tried the door at the bottom. Locked as well. Looking up, I saw the ceiling of the pit swooping down on me.
It had to be the mechanism, I thought. The doors were locked until the crushing process was complete.
And I was the one standing inside the crusher!