"Ah!" said Mr. Lawley. "Thereby hangs a very curious tale of
coincidences. The police, of course, when they found that there was so
simple a means of identification as a thumb-mark, wished to take
thumb-prints of all the employees in the works; but this Mr. Hornby
refused to sanction--rather quixotically, as it seems to me--saying that
he would not allow his nephews to be subjected to such an indignity. Now
it was, naturally, these nephews in whom the police were chiefly
interested, seeing that they alone had had the handling of the keys, and
considerable pressure was brought to bear upon Mr. Hornby to have the
thumb-prints taken.

"However, he was obdurate, scouting the idea of any suspicion attaching
to either of the gentlemen in whom he had reposed such complete
confidence and whom he had known all their lives, and so the matter
would probably have remained a mystery but for a very odd circumstance.

"You may have seen on the bookstalls and in shop windows an appliance
called a 'Thumbograph,' or some such name, consisting of a small book of
blank paper for collecting the thumb-prints of one's friends, together
with an inking pad."

"I have seen those devices of the Evil One," said Thorndyke, "in fact, I
have one, which I bought at Charing Cross Station."

"Well, it seems that some months ago Mrs. Hornby, the wife of John
Hornby, purchased one of these toys--" "As a matter of fact,"
interrupted Reuben, "it was my cousin Walter who bought the thing and
gave it to her."

"Well, that is not material," said Mr. Lawley (though I observed that