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 Thorndyke made a note of the fact in his book); "at any rate, Mrs.
Hornby became possessed of one of these appliances and proceeded to fill it with the thumb-prints of her friends, including her two nephews.

Now it happened that the detective in charge of this case called yesterday at Mr.Hornby's house when the latter was absent from home, and took the opportunity of urging her to induce her husband to consent to have the thumb-prints of her nephews taken for the inspection of the experts at Scotland Yard.

He pointed out that the procedure was really necessary, not only in the interests of justice but in the interests of the young men themselves, who were regarded with considerable suspicion by the police, which suspicion would be completely removed if it could be shown by actual comparison that the thumb-print could not have been made by either of them.

Moreover, it seemed that both the young men had expressed their willingness to have the test applied, but had been forbidden by their uncle.