“I quite understand. And I only hesitated just now,” he went on, his words coming much more slowly, as though he felt he had already said too much, “because I wished to be quite sure it was no mere curiosity, but an actual sense of necessity that dictated this horrible experiment.”

“It is your safety, and that of your household, and of your sister, that is at stake,” replied the doctor. “Once I have seen , I hope to discover whence this elemental comes, and what its real purpose is.”

Colonel Wragge signified his assent with a bow.

“And the moon will help us,” the other said, “for it will be full in the early hours of the morning, and this kind of elemental-being is always most active at the period of full moon. Hence, you see, the clue furnished by your diary.”