“I see some particles of metal—­a white metal apparently—­and a number of fragments of woody fibre and starch granules, but I don’t recognize the starch.  It is not wheat-starch, nor rice, nor potato.  Do you make out what it is?”

[Illustration:  FLUFF FROM KEY-BARREL, MAGNIFIED 77 DIAMETERS.]

Thorndyke chuckled.  “Experientia does it,” said he.  “You will have, Jervis, to study the minute properties of dust and dirt.  Their evidential value is immense.  Let us have another look at that starch; it is all alike, I suppose.”

It was; and Thorndyke had just ascertained the fact when the door burst open and Mrs. Haldean entered the room, followed by Mrs. Hanshaw and the police inspector.  The former lady regarded my colleague with a glance of extreme disfavour.

“We heard that you had come here, sir,” said she, “and we supposed you were engaged in searching for my poor child.  But it seems we were mistaken, since we find you here amusing yourselves fiddling with these nonsensical instruments.”

“Perhaps, Mabel,” said Mrs. Hanshaw stiffly, “it would be wiser, and infinitely more polite, to ask if Dr. Thorndyke has any news for us.”

“That is undoubtedly so, madam,” agreed the inspector, who had apparently suffered also from Mrs. Haldean’s impulsiveness.

“Then perhaps,” the latter lady suggested, “you will inform us if you have discovered anything.”

“I will tell you.” replied Thorndyke, “all that we know.  The child was abducted by the man who occupied this house, and who appears to have watched him from an upper window, probably through a glass.  This man lured the child into the wood by blowing this bird-call; he met him in the wood, and induced him—­by some promises, no doubt—­to come with him.  He picked the child up and carried him—­on his back, I think—­up to the house, and brought him in through the front door, which he locked after him.  He gave the boy this clock and the bird-call to amuse him while he went upstairs and packed his trunk.  He took the trunk out through the back door and down the garden to the shed there, in which he had a motor-car.  He got the car out and came back for the boy, whom he carried down to the car, locking the back door after him.  Then he drove away.”

“You know he has gone,” cried Mrs. Haldean, “and yet you stay here playing with these ridiculous toys.  Why are you not following him?”

“We have just finished ascertaining the facts,” Thorndyke replied calmly, “and should by now be on the road if you had not come.”

Here the inspector interposed anxiously.  “Of course, sir, you can’t give any description of the man.  You have no clue to his identity, I suppose?”

“We have only his footprints,” Thorndyke answered, “and this fluff which I raked out of the barrel of his latchkey, and have just been examining.  From these data I conclude that he is a rather short and thin man, and somewhat lame.  He walks with the aid of a thick stick, which has a knob, not a crook, at the top, and which he carries in his left hand.  I think that his left leg has been amputated above the knee, and that he wears an artificial limb.  He is elderly, he shaves his beard, has white hair dyed a greyish black, is partly bald, and probably combs a wisp of hair over the bald place; he takes snuff, and carries a leaden comb in his pocket.”