“It has, Inspector,” I agreed; “but I don’t know that the fact enlightens us very much; for it merely indicates that the man whom you declare to be the central figure of the conspiracy is only a secondary figure, and that all we know about the person whom we may regard as the prime mover is that she is a woman—­apparently possessing supernormal eyes which glitter in the dark.  She is also associated in some way with the figure of Bast.  What is her relation to Dr. Damar Greefe and in what way is she interested in the destruction of the Coverly family?”

Gatton smoked in silence for a while, staring at me reflectively, then: 

“If we knew that, Mr. Addison,” he said, “we should know all there is to know about ‘the Oritoga mystery.’  But I think we should have advanced a long step towards this information if we could apprehend the Eurasian.  Of course we have gathered up all the ragged details of the Red House incident:  I refer to the carter who delivered the crate and collected it in the morning, of the caterer who supplied the supper and so forth.  As I had fully expected, none of the evidence helped us at all.”

“‘The voice,’” I began.

“Exactly!  The same ‘voice’ beyond a doubt, and the whole thing worked through the means of district messengers and others, telephonically instructed.  No one appeared throughout, Mr. Addison.”

“Yet,” I said deliberately, “there was one point at which some one must have appeared—­”

“Yes,” he interrupted, “some one dragged the body out of that supper-room, down to the garage, and packed it in the crate.”

“You have definitely convinced yourself that the telephone device was practiced there?”

“Beyond question.  Haven’t you seen the exchange number?  That plug where at some time a gas-fitting had been fixed up in the wall—­you remember?—­proved on investigation to communicate with an empty room adjoining.  The gas cylinder was placed there of course, and the telephone in the recess of the supper-room, where, fastened in by the velvet curtain, any one using the poison installation would be suffocated almost immediately.”

“Good God, Gatton!” I cried.  “It’s a horrible business, and for my own part I have no idea what the next step should be.”

“I’m a bit doubtful, myself,” admitted Gatton; “but you know the line of reasoning which has led me to the conclusion that these people possess a base of operations somewhere in this district.  I am having the neighborhood scoured pretty thoroughly, and I think it is merely a question of time, now, for us to hem in the wanted man—­”

“And the wanted woman!” I added.

We were interrupted by a knock at the study door, and Coates came in with the evening mail.

“Excuse me, Gatton,” I said—­for I had observed that one of the letters was from Isobel.

Eagerly I tore open the envelope ... and what I read struck a sudden chill to my heart.  Looking up: