Meanwhile, the master criminal was busily engaged in putting the finishing touches to a final scheme of fiendish ingenuity for the absolute destruction of Craig Kennedy.

He had been at work in a small room, fitted up as a sort of laboratory, in the mysterious house which now served as his headquarters.

On all sides were shelves filled with bottles of deadly liquids and scientific apparatus for crime. Jars of picric acid, nitric acid, carboys of other chemicals, packages labelled gunpowder, gun cotton and nitroglycerine, as well as carefully stoppered bottles of prussic acid, and the cyanides, a.r.s.enic and other poisons made the place bear the look of a veritable devil's workshop.

Clutching Hand, at a bench in one corner, had just completed an infernal machine of diabolical cunning, and was wrapping it carefully in paper to make an innocent package.

He was interrupted by a knock at the door. Laying down the bomb he went to answer the summons with a stealthy movement. There stood Long Sin, who had disguised himself as a Chinese laundryman.

"On time--good!" growled Clutching Hand surlily as he closed the door with equal care.

No time was wasted in useless formalities.

"This is a bomb," he went on, pointing to the package. "Carry it carefully. On no account let it slip, or you are a dead man. It must be in Kennedy's laboratory before night. Understand? Can you arrange it?"

Long Sin looked the dangerous package over, then with an impa.s.sive look, replied, "Have no fear. I can do it. It will be in the laboratory within an hour. Trust me."

Long Sin nodded sagely, while Clutching Hand growled his approval as he opened the door and let out the Chinaman. Long Sin departed as stealthily as he had come, the frightful engine of destruction hugged up carefully under his wide-sleeved coolie shirt.

For a moment Clutching Hand gave himself up to the exquisite contemplation of what he had just done, then turned to clean up his workshop.

In Kennedy's laboratory I was watching Craig make some experiments with a new X-ray apparatus which had just arrived, occasionally looking through the fluoroscope when he was examining some unusually interesting object.

We were oblivious to the pa.s.sage of time, and only a call over our speaking tube diverted our attention.

I opened the door and a few seconds later Long Sin himself entered.

Kennedy looked up inquiringly as the Chinaman approached, holding out a package which he carried.

"A bomb," he said, in the most matter of fact way. "I promised to have it placed in your laboratory before night."

The placid air with which the grotesque looking Chinaman imparted this astounding information was in itself preposterous. His actions and words as he laid the package down gingerly on the laboratory table indicated that he was telling the truth.

Kennedy and I stared at each other in blank amazement for a moment.

Then the humor of the thing struck us both and we laughed outright.

Clutching Hand had told him to deliver it--and he had done so!

Hastily I filled a pail with water and brought it to Kennedy.

"If it is really a bomb," I remarked, "why not put the thing out of commission?"

"No, no, Walter," he cried quickly, shaking his head. "If it's a chemical bomb, the water might be just the thing to make the chemicals run together and set it off. No, let us see what the new X-ray machine can tell us, first."

He took the bomb and carefully placed it under the wonderful rays, then with the fluoroscope over his eyes studied the shadow cast by the rays on its sensitive screen. For several minutes he continued safely studying it from every angle, until he thoroughly understood it.

"It's a bomb, sure enough," Craig exclaimed, looking up from it at last to me. "It's timed by an ingenious and noiseless little piece of clockwork, in there, too. And it's powerful enough to blow us all, the laboratory included, to kingdom come."

As he spoke, and before I could remonstrate with him, he took the infernal machine and placed it on a table where he set to work on the most delicate and dangerous piece of dissection of which I have ever heard.

Carefully unwrapping the bomb and uns.c.r.e.w.i.n.g one part while he held another firm, he finally took out of it a bottle of liquid and some powder. Then he placed a few grains of the powder on a dish and dropped on it a drop or two of the liquid. There was a bright flash, as the powder ignited instantly.

"Just what I expected," commented Kennedy with a nod, as he examined the clever workmanship of the bomb.

One thing that interested him was that part of the contents had been wrapped in paper to keep them in place. This paper he was now carefully examining with a hand lens.

As nearly as I could make it out, the paper contained part of a typewritten chemical formula, which read:

TINCTURE OF IODINE

THREE PARTS OF---

He looked up from his study of the microscope to Long Sin.

"Tell me just how it happened that you got this bomb," he asked.

Without hesitation, the Chinaman recited the circ.u.mstances, beginning with the note by which he had been summoned.

"A note?" repeated Kennedy, eagerly. "Was it typewritten?"

Long Sin reached into his pocket and produced the note itself, which he had not burned.

As Craig studied the typewritten message from the Clutching Hand I could see that he was growing more and more excited.

"At last he has given us something typewritten," he exclaimed. "To most people, I suppose, it seems that typewriting is the best way to conceal ident.i.ty. But there are a thousand and one ways of identifying typewriting. Clutching Hand knew that. That was why he was so careful to order this note destroyed. As for the bomb, he figured that it would destroy itself."

He was placing one piece of typewriting after another under the lens, scrutinizing each letter closely.

"Look, Walter," he remarked at length, taking a fine tipped pencil and pointing at the distinguishing marks as he talked, "You will notice that all the 'T's' in this note are battered and faint as well as just a trifle out of alignment. Now I will place the paper from the bomb under the lens and you will also see that the 'T's' in the sc.r.a.p of formula have exactly the same appearance. That indicated, without the possibility of a doubt, taken in connection with a score of other peculiarities in the letters which I could pick out that both were written on the same typewriter. I have selected the 'T' because it is the most marked."

I strained my eyes to look. Sure enough, Kennedy was right. There was that unmistakable ident.i.ty between the T's in the formula and the note.

Kennedy had been gazing at the floor, his face puckered in thought as I looked. Suddenly he slapped his hands together, as if he had made a great discovery.

"I've struck it!" he exclaimed, jumping up. "I was wondering where I had seen typewriting that reminds me of this. Walter, get on your coat and hat. We are on the right trail at last."

With Long Sin we hurried out of the laboratory, leaving him at the nearest taxicab stand, where we jumped into a waiting car.

"It is the clue of the battered 'T's,'" Craig muttered.

Aunt Josephine was in the library knitting when the butler, Jennings, announced us. We were admitted at once, for Aunt Josephine had never quite understood what was the trouble between Elaine and Craig, and had a high regard for him.

"Where is--Miss Dodge?" inquired Kennedy, with suppressed excitement as we entered.