“Yes, some of us are a little too much inclined to be cock-sure, Mr. Holmes,” said Lestrade.  The man’s insolence was maddening, but we could not resent it.

“What a providential thing that this young man should press his right thumb against the wall in taking his hat from the peg!  Such a very natural action, too, if you come to think of it.”  Holmes was outwardly calm, but his whole body gave a wriggle of suppressed excitement as he spoke.

“By the way, Lestrade, who made this remarkable discovery?”

“It was the housekeeper, Mrs. Lexington, who drew the night constable’s attention to it.”

“Where was the night constable?”

“He remained on guard in the bedroom where the crime was committed, so as to see that nothing was touched.”

“But why didn’t the police see this mark yesterday?”

“Well, we had no particular reason to make a careful examination of the hall.  Besides, it’s not in a very prominent place, as you see.”

“No, no—­of course not.  I suppose there is no doubt that the mark was there yesterday?”

Lestrade looked at Holmes as if he thought he was going out of his mind.  I confess that I was myself surprised both at his hilarious manner and at his rather wild observation.

“I don’t know whether you think that McFarlane came out of jail in the dead of the night in order to strengthen the evidence against himself,” said Lestrade.  “I leave it to any expert in the world whether that is not the mark of his thumb.”

“It is unquestionably the mark of his thumb.”

“There, that’s enough,” said Lestrade.  “I am a practical man, Mr. Holmes, and when I have got my evidence I come to my conclusions.  If you have anything to say, you will find me writing my report in the sitting-room.”

Holmes had recovered his equanimity, though I still seemed to detect gleams of amusement in his expression.

“Dear me, this is a very sad development, Watson, is it not?” said he.  “And yet there are singular points about it which hold out some hopes for our client.”

“I am delighted to hear it,” said I, heartily.  “I was afraid it was all up with him.”

“I would hardly go so far as to say that, my dear Watson.  The fact is that there is one really serious flaw in this evidence to which our friend attaches so much importance.”

“Indeed, Holmes!  What is it?”

“Only this:  that I know that that mark was not there when I examined the hall yesterday.  And now, Watson, let us have a little stroll round in the sunshine.”

With a confused brain, but with a heart into which some warmth of hope was returning, I accompanied my friend in a walk round the garden.  Holmes took each face of the house in turn, and examined it with great interest.  He then led the way inside, and went over the whole building from basement to attic.  Most of the rooms were unfurnished, but none the less Holmes inspected them all minutely.  Finally, on the top corridor, which ran outside three untenanted bedrooms, he again was seized with a spasm of merriment.