missing altogether on
the paper. So it is in the photograph."

Almost like a schoolboy in his glee, he was comparing the little round
circles made by the metal insertions in an "anti-skid" automobile tire.
Time and again I had seen imprints like that left in the dust and grease
of an asphalted street or the mud of a road. It had never occurred to me
that they might be used in any way. Yet here Craig was, calmly tracing
out the similarity before my very eyes, identifying the marks made in
the photograph with the prints left on the bits of paper.

As I followed him, I had a most curious feeling of admiration for his
genius. "Craig," I cried, "that's the thumb-print of an automobile."

"There speaks the yellow journalist," he answered merrily. "'Thumb Print
System Applied to Motor Cars'--I can see the Sunday feature story
you have in your mind with that headline already. Yes, Walter, that's
precisely what this is. The Berlin police have used it a number of times
with the most startling results."

"But, Craig," I exclaimed suddenly, "the paper prints, where did you get
them? What machine is it?"

"It's one not very far from here," he answered sententiously, and I saw
he would say nothing more that might fix a false suspicion on anyone.
Still, my curiosity was so great that if there had been an opportunity I
certainly should have tried out his plan on all the cars in the Fletcher
garage.

Kennedy would say nothing more, and we ate our luncheon in silence.
Fletcher, who had decided to lunch with the Greenes, called Kennedy up
on the telephone to tell him it would be all right for him to call on
Miss Bond later in the afternoon.

"And I may bring over the apparatus I once described to you to determine
just what her nervous condition is?" he asked. Apparently the answer was
yes, for Kennedy hung up the receiver with a satisfied, "Good-bye."

"Walter, I want you to come along with me this afternoon as my
assistant. Remember I'm now Dr. Kennedy, the nerve specialist, and you
are Dr. Jameson, my colleague, and we are to be in consultation on a
most important case."

"Do you think that's fair?" I asked hotly, "to take that girl off her
guard, to insinuate yourself into her confidence as a medical adviser,
and worm out of her some kind of fact incriminating someone? I suppose
that's your plan, and I don't like the ethics, or rather the lack of
ethics, of the thing."

"Now think a minute, Walter. Perhaps I am wrong; I don