Colonel Wragge meanwhile grew more and more fidgety.  From time to time he turned towards my companion, as though about to speak, yet always changing his mind at the last moment.  Once he went over and opened the door suddenly, apparently to see if any one were listening at the keyhole, for he disappeared a moment between the two doors, and I then heard him open the outer one.  He stood there for some seconds and made a noise as though he were sniffing the air like a dog.  Then he closed both doors cautiously and came back to the fireplace.  A strange excitement seemed growing upon him.  Evidently he was trying to make up his mind to say something that he found it difficult to say.  And John Silence, as I rightly judged, was waiting patiently for him to choose his own opportunity and his own way of saying it.  At last he turned and faced us, squaring his great shoulders, and stiffening perceptibly.

Dr. Silence looked up sympathetically.

“Your own experiences help me most,” he observed quietly.

“The fact is,” the Colonel said, speaking very low, “this past week there have been outbreaks of fire in the house itself.  Three separate outbreaks—­and all—­in my sister’s room.”

“Yes,” the doctor said, as if this was just what he had expected to hear.

“Utterly unaccountable—­all of them,” added the other, and then sat down.  I began to understand something of the reason of his excitement.  He was realising at last that the “natural” explanation he had held to all along was becoming impossible, and he hated it.  It made him angry.

“Fortunately,” he went on, “she was out each time and does not know.  But I have made her sleep now in a room on the ground floor.”

“A wise precaution,” the doctor said simply.  He asked one or two questions.  The fires had started in the curtains—­once by the window and once by the bed.  The third time smoke had been discovered by the maid coming from the cupboard, and it was found that Miss Wragge’s clothes hanging on the hooks were smouldering.  The doctor listened attentively, but made no comment.

“And now can you tell me,” he said presently, “what your own feeling about it is—­your general impression?”

“It sounds foolish to say so,” replied the soldier, after a moment’s hesitation, “but I feel exactly as I have often felt on active service in my Indian campaigns:  just as if the house and all in it were in a state of siege; as though a concealed enemy were encamped about us—­in ambush somewhere.”  He uttered a soft nervous laugh.  “As if the next sign of smoke would precipitate a panic—­a dreadful panic.”

The picture came before me of the night shadowing the house, and the twisted pine trees he had described crowding about it, concealing some powerful enemy; and, glancing at the resolute face and figure of the old soldier, forced at length to his confession, I understood something of all he had been through before he sought the assistance of John Silence.