As Thorndyke’s description proceeded, the inspector’s mouth gradually opened wider and wider, until he appeared the very type and symbol of astonishment.  But its effect on Mrs. Haldean was much more remarkable.  Rising from her chair, she leaned on the table and stared at Thorndyke with an expression of awe—­even of terror; and as he finished she sank back into her chair, with her hands clasped, and turned to Mrs. Hanshaw.

“Jane!” she gasped, “it is Percy—­my brother-in-law!  He has described him exactly, even to his stick and his pocket-comb.  But I thought he was in Chicago.”

“If that is so,” said Thorndyke, hastily repacking his case, “we had better start at once.”

“We have the dogcart in the road,” said Mrs. Hanshaw.

“Thank you,” replied Thorndyke.  “We will ride on our bicycles, and the inspector can borrow Willett’s.  We go out at the back by the cart-track, which joins the road farther on.”

“Then we will follow in the dogcart,” said Mrs. Haldean.  “Come, Jane.”

The two ladies departed down the path, while we made ready our bicycles and lit our lamps.

“With your permission, inspector,” said Thorndyke, “we will take the key with us.”

“It’s hardly legal, sir,” objected the officer.  “We have no authority.”

“It is quite illegal,” answered Thorndyke; “but it is necessary; and necessity—­like your military J.P.—­knows no law.”

The inspector grinned and went out, regarding me with a quivering eyelid as Thorndyke locked the door with his skeleton key.  As we turned into the road, I saw the light of the dogcart behind us, and we pushed forward at a swift pace, picking up the trail easily on the soft, moist road.

“What beats me,” said the inspector confidentially, as we rode along, “is how he knew the man was bald.  Was it the footprints or the latchkey?  And that comb, too, that was a regular knock-out.”

These points were, by now, pretty clear to me.  I had seen the hairs with their atrophied bulbs—­such as one finds at the margin of a bald patch; and the comb was used, evidently, for the double purpose of keeping the bald patch covered and blackening the sulphur-charged hair.  But the knobbed stick and the artificial limb puzzled me so completely that I presently overtook Thorndyke to demand an explanation.

“The stick,” said he, “is perfectly simple.  The ferrule of a knobbed stick wears evenly all round; that of a crooked stick wears on one side—­the side opposite the crook.  The impressions showed that the ferrule of this one was evenly convex; therefore it had no crook.  The other matter is more complicated.  To begin with, an artificial foot makes a very characteristic impression, owing to its purely passive elasticity, as I will show you to-morrow.  But an artificial leg fitted below the knee is quite secure, whereas one fitted above the knee—­that is, with an artificial knee-joint worked by a spring—­is