"I saw something," I replied, "but I couldn't tell you what it
was."

"Well," he explained slowly as I opened my eyes wide in amazement
at the minuteness of his researches, "those were the marks of the
tire of an automobile that had been run up into the bushes from
the road. You know every automobile tire leaves its own
distinctive mark, its thumb print, as it were. When I have
developed my films, you will see that the marks that have been
left there are precisely like those left by the make of tires used
on Warrington's car, according to the advertisement sent out by
McBirney. Of course, that mere fact alone doesn't prove anything.
Many cars may use that make of tires. Still, it is an interesting
coincidence, and if the make had been different I should not feel
half so encouraged about going ahead with this clew. We can't say
anything definite, however, until I can compare the actual marks
made by the tires on the stolen car with these marks which I have
photographed and preserved."

If any one other than Garrick had conceived such a notion as the
"thumb print" of an automobile tire, I might possibly have
ventured to doubt it. As it was it gave food enough for thought to
last the remainder of the journey back to town.




CHAPTER IV

THE LIQUID BULLET