I did so, and driven by the draught a coil of gray smoke swirled down the corridor, while the dry straw crackled and flamed.

“Now we must see if we can find this witness for you, Lestrade.  Might I ask you all to join in the cry of ‘Fire!’?  Now then; one, two, three——­”

“Fire!” we all yelled.

“Thank you.  I will trouble you once again.”

“Fire!”

“Just once more, gentlemen, and all together.”

“Fire!” The shout must have rung over Norwood.

It had hardly died away when an amazing thing happened.  A door suddenly flew open out of what appeared to be solid wall at the end of the corridor, and a little, wizened man darted out of it, like a rabbit out of its burrow.

“Capital!” said Holmes, calmly.  “Watson, a bucket of water over the straw.  That will do!  Lestrade, allow me to present you with your principal missing witness, Mr. Jonas Oldacre.”

The detective stared at the newcomer with blank amazement.  The latter was blinking in the bright light of the corridor, and peering at us and at the smouldering fire.  It was an odious face—­crafty, vicious, malignant, with shifty, light-gray eyes and white lashes.

“What’s this, then?” said Lestrade, at last.  “What have you been doing all this time, eh?”

Oldacre gave an uneasy laugh, shrinking back from the furious red face of the angry detective.

“I have done no harm.”

“No harm?  You have done your best to get an innocent man hanged.  If it wasn’t for this gentleman here, I am not sure that you would not have succeeded.”

The wretched creature began to whimper.

“I am sure, sir, it was only my practical joke.”

“Oh! a joke, was it?  You won’t find the laugh on your side, I promise you.  Take him down, and keep him in the sitting-room until I come.  Mr. Holmes,” he continued, when they had gone, “I could not speak before the constables, but I don’t mind saying, in the presence of Dr. Watson, that this is the brightest thing that you have done yet, though it is a mystery to me how you did it.  You have saved an innocent man’s life, and you have prevented a very grave scandal, which would have ruined my reputation in the Force.”

Holmes smiled, and clapped Lestrade upon the shoulder.

“Instead of being ruined, my good sir, you will find that your reputation has been enormously enhanced.  Just make a few alterations in that report which you were writing, and they will understand how hard it is to throw dust in the eyes of Inspector Lestrade.”

“And you don’t want your name to appear?”

“Not at all.  The work is its own reward.  Perhaps I shall get the credit also at some distant day, when I permit my zealous historian to lay out his foolscap once more—­eh, Watson?  Well, now, let us see where this rat has been lurking.”

A lath-and-plaster partition had been run across the passage six feet from the end, with a door cunningly concealed in it.  It was lit within by slits under the eaves.  A few articles of furniture and a supply of food and water were within, together with a number of books and papers.