Here Mrs. Hornby drew forth a lace-edged handkerchief and mopped her eyes.

“I am sure Dr. Thorndyke will be very much interested to see this little book of yours,” said I, with a view to stemming the tide of her reflections.

“Oh, the ‘Thumbograph,’” she replied.  “Yes, I will let him have it with the greatest pleasure.  I am so glad he wishes to see it; it makes one feel hopeful to know that he is taking so much interest in the case.  Would you believe it, Dr. Jervis, those detective people actually wanted to keep it to bring up in evidence against the poor boy.  My ‘Thumbograph,’ mind you.  But I put my foot down there and they had to return it.  I was resolved that they should not receive any assistance from me in their efforts to involve my nephew in this horrible affair.”

“Then, perhaps,” said Miss Gibson, “you might give Dr. Jervis the ‘Thumbograph’ and he can hand it to Dr. Thorndyke.”

“Of course I will,” said Mrs. Hornby; “instantly; and you need not return it, Dr. Jervis.  When you have finished with it, fling it into the fire.  I wish never to see it again.”

But I had been considering the matter, and had come to the conclusion that it would be highly indiscreet to take the book out of Mrs. Hornby’s custody, and this I now proceeded to explain.

“I have no idea,” I said, “for what purpose Dr. Thorndyke wishes to examine the ‘Thumbograph,’ but it occurs to me that he may desire to put it in evidence, in which case it would be better that it should not go out of your possession for the present.  He merely commissioned me to ask for your permission to take a photograph of it.”

“Oh, if he wants a photograph,” said Mrs. Hornby, “I could get one done for him without any difficulty.  My nephew Walter would take one for us, I am sure, if I asked him.  He is so clever, you know—­is he not, Juliet, dear?”

“Yes, aunt,” replied Miss Gibson quickly, “but I expect Dr. Thorndyke would rather take the photograph himself.”

“I am sure he would,” I agreed.  “In fact, a photograph taken by another person would not be of much use to him.”

“Ah,” said Mrs. Hornby in a slightly injured tone, “you think Walter is just an ordinary amateur; but if I were to show you some of the photographs he has taken you would really be surprised.  He is remarkably clever, I assure you.”

“Would you like us to bring the book to Dr. Thorndyke’s chambers?” asked Miss Gibson.  “That would save time and trouble.”

“It is excessively good of you—­” I began.

“Not at all.  When shall we bring it?  Would you like to have it this evening?”

“We should very much,” I replied.  “My colleague could then examine it and decide what is to be done with it.  But it is giving you so much trouble.”

“It is nothing of the kind,” said Miss Gibson.  “You would not mind coming with me this evening, would you, aunt?”

“Certainly not, my dear,” replied Mrs. Hornby, and she was about to enlarge on the subject when Miss Gibson rose and, looking at her watch, declared that she must start on her errand at once.  I also rose to make my adieux, and she then remarked—­