I shut the chancel gate, and we both stood well to one side. I
took the spear-like lever, and gave the gate a little push, so that it
opened. Instantly there was a loud thud, and something sang through the
air, striking the bottom wall of the Chapel. It was the dagger. I
showed Jarnock then that the other half of the post had sprung back
into place, making the whole post as thick as the one upon the
right-hand side of the gate.

"There!" I said, turning to the young man and tapping the divided post.
"There's the 'invisible' thing that used the dagger, but who the deuce is
the person who sets the trap?" I looked at him keenly as I spoke.

"My father is the only one who has a key," he said. "So it's practically
impossible for anyone to get in and meddle."

I looked at him again, but it was obvious that he had not yet reached out
to any conclusion.

"See here, Mr. Jarnock," I said, perhaps rather curter than I should have
done, considering what I had to say. "Are you quite sure that Sir Alfred
is quite balanced--mentally?"

"He looked at me, half frightenedly and flushing a little. I realized
then how badly I put it.

"'I--I don't know,' he replied, after a slight pause and was then silent,
except for one or two incoherent half remarks.

"'Tell the truth,' I said. 'Haven't you suspected something, now and
again? You needn't be afraid to tell me.'

"'Well,' he answered slowly, 'I'll admit I've thought Father a little--a
little strange, perhaps, at times. But I've always tried to think I was
mistaken. I've always hoped no one else would see it. You see, I'm very
fond of the old guvnor.'

"I nodded.

"'Quite right, too,' I said. 'There's not the least need to make any kind
of scandal about this. We must do something, though, but in a quiet way.
No fuss, you know. I should go and have a chat with your father, and tell
him we've found out about this thing.' I touched the divided post.

"Young Jarnock seemed very grateful for my advice and after shaking my
hand pretty hard, took my key, and let himself out of the Chapel. He came
back in about an hour, looking rather upset. He told me that my
conclusions were perfectly correct. It was Sir Alfred Jarnock who had set
the trap, both on the night that the butler was nearly killed, and on the
past night. Indeed, it seemed that the old gentleman had set it every
night for many years. He had learnt of its existence from an old
manuscript book in the Castle library. It had b