“Here we are in a worse mystery than ever,” grumbled Andrews.  “We have caught a prisoner, but the body is gone, and we can’t even show that he was an accomplice.”

“What were you writing?” I asked Craig, endeavouring to change the subject to one more promising.

“Just copying the peculiar shape of those marks on Phelps’ arm.  Perhaps we can improve on the finger-print method of identification.  Those were the marks of human teeth.”

He was glancing casually at his sketch as he displayed it to us.  I wondered whether he really expected to obtain proof of the identity of at least one of the ghouls by the tooth-marks.

“It shows eight teeth, one of them decayed,” he remarked.  “By the way, there’s no use watching here any longer.  I have some more work to do in the laboratory which will keep me another day.  To-morrow night I shall be ready.  Andrews, in the mean time I leave the shadowing of Dana to you, and with the help of Jameson I want you to arrange to have all those connected with the case at my laboratory to-morrow night without fail.”

Andrews and I had to do some clever scheming to bring pressure to bear on the various persons interested to insure their attendance, now that Craig was ready to act.  Of course there was no difficulty in getting Dana Phelps.  Andrews’s shadows reported nothing in his actions of the following day that indicated anything.  Mrs. Phelps came down to town by train and Doctor Forden motored in.  Andrews even took the precaution to secure Shaughnessy and the trained nurse, Miss Tracy, who had been with Montague Phelps during his illness but had not contributed anything toward untangling the case.  Andrews and myself completed the little audience.

We found Kennedy heating a large mass of some composition such as dentists use in taking impressions of the teeth.

“I shall be ready in a moment,” he excused himself, still bending over his Bunsen flame.  “By the way, Mr. Phelps, if you will permit me.”

He had detached a wad of the softened material.  Phelps, taken by surprise, allowed him to make an impression of his teeth, almost before he realised what Kennedy was doing.  The precedent set, so to speak, Kennedy approached Doctor Forden.  He demurred, but finally consented.  Mrs. Phelps followed, then the nurse, and even Shaughnessy.

With a quick glance at each impression, Kennedy laid them aside to harden.

“I am ready to begin,” he remarked at length, turning to a peculiar looking instrument, something like three telescopes pointing at a centre in which was a series of glass prisms.

“These five senses of ours are pretty dull detectives sometimes,” Kennedy began.  “But I find that when we are able to call in outside aid we usually find that there are no more mysteries.”

He placed something in a test-tube in line before one of the barrels of the telescopes, near a brilliant electric light.