They were locked in the room while some devilment was going on in the rest of the house.

That they knew.

But what it might be, what form it might take, they had not the remotest idea.
They were too distracted to notice the injured man, now alert in his chair, or the Doctor's odd attitude of listening, above the rattle and banging of the storm.
But it was not until Miss Cornelia took the candle and proceeded toward the hall door to examine it that the full horror of the situation burst upon them.
Neatly fastened to the white panel of the door, chest high and hardly more than just dead, was the body of a bat.
Of what happened thereafter no one afterward remembered the details.

To be shut in there at the mercy of one who knew no mercy was intolerable.
It was left for Miss Cornelia to remember her own revolver, lying unnoticed on the table since the crime earlier in the evening, and to suggest its use in shattering the lock.

Just what they had expected when the door was finally opened they did not know.