The envelope was empty. We looked at each other a moment in silence.

What had been done with the plans?

Suddenly a bell rang, startling me beyond measure. It was, however, only the telephone, of which an extension reached up into the attic-a.r.s.enal. Some one, who did not know that we were there, was evidently calling up.

Kennedy quickly unhooked the receiver with a hasty motion to me to be silent.

"h.e.l.lo," I heard him answer. "Yes, this is it."

He had disguised his voice. I waited anxiously and watched his face to gather what response he received.

"The deuce!" he exclaimed, with his hand over the transmitter so that his voice would not be heard at the other end of the line.

"What's the matter?" I asked eagerly.

"It was Mrs. Annenberg--I am sure. But she was too keen for me. She caught on. There must be some pa.s.sword or form of expression that they use, which we don't know, for she hung up the receiver almost as soon as she heard me."

Kennedy waited a minute or so. Then he whistled into the transmitter.

It was done apparently to see whether there was anyone listening. But there was no answer.

"Operator, operator!" he called insistently, moving the hook up and down. "Yes, operator. Can you tell me what number that was which just called?"

He waited impatiently.

"Bleecker--7l80," he repeated after the girl. "Thank you. Information, please."

Again we waited, as Craig tried to trace the call up.

"What is the street address of Bleecker, 7180?" he asked. "Five hundred and one East Fifth--a tenement. Thank you."

"A tenement?" I repeated blankly.

"Yes," he cried, now for the first time excited. "Don't you begin to see the scheme? I'll wager that Baron Kreiger has been lured to New York to purchase the electro-magnetic gun which they have stolen from Fortescue and the British. That is the bait that is held out to him by the woman. Call up Miss Lowe at the laboratory and see if she knows the place."

I gave central the number, while he fell to at the little secret drawer of the desk again. The grinding of the wheels of a pa.s.sing trolley interfered somewhat with giving the number and I had to wait a moment.

"Ah--Walter--here's the list!" almost shouted Kennedy, as he broke open a black-j.a.panned dispatch box in the desk.

I bent over it, as far as the slack of the telephone wire of the receiver at my ear would permit. Annenberg had worked with amazing care and neatness on the list, even going so far as to draw at the top, in black, a death's head. The rest of it was elaborately prepared in flaming red ink.

Craig gasped to observe the list of world-famous men marked for destruction in London, Paris, Berlin, Rome, Vienna, St. Petersburg, and even in New York and Washington.

"What is the date set?" I asked, still with my ear glued to the receiver.

"To-night and to-morrow," he replied, stuffing the fateful sheet into his pocket.

Rummaging about in the drawer of the table, I had come to a package of gold-tipped cigarettes which had interested me and I had left them out.

Kennedy was now looking at them curiously.

"What is to be the method, do you suppose?" I asked.

"By a poison that is among the most powerful, approaching even cyanogen," he replied confidently, tapping the cigarettes. "Do you smell the odor in this room? What is it like?"

"Stale tobacco," I replied.

"Exactly--nicotine. Two or three drops on the mouth-end of a cigar or cigarette. The intended victim thinks it is only natural. But it is the purest form of the deadly alkaloid--fatal in a few minutes, too."

He examined the thin little cigarettes more carefully. "Nicotine," he went on, "was about the first alkaloid that was recovered from the body by chemical a.n.a.lysis in a homicide case. That is the penetrating, persistent odor you smelled at Fortescue's and also here. It's a very good poison--if you are not particular about being discovered. A pound of ordinary smoking tobacco contains from a half to an ounce of it. It is almost entirely consumed by combustion; otherwise a pipeful would be fatal. Of course they may have thought that investigators would believe that their victims were inveterate smokers. But even the worst tobacco fiend wouldn't show traces of the weed to such an extent."

Miss Lowe answered at last and Kennedy took the telephone.

"What is at five hundred and one East Fifth?" he asked.

"A headquarters of the Group in the city," she answered. "Why?"

"Well, I believe that the plans of that gun are there and that the Baron--"

"You d.a.m.ned spies!" came a voice from behind us.

Kennedy dropped the receiver, turning quickly, his automatic gleaming in his hand.

There was just a glimpse of a man with glittering bright blue eyes that had an almost fiendish, baleful glare. An instant later the door which had so unexpectedly opened banged shut, we heard a key turn in the lock--and the man dropped to the floor before even Kennedy's automatic could test its ability to penetrate wood on a chance at hitting something the other side of it.

We were prisoners!

My mind worked automatically. At this very moment, perhaps, Baron Kreiger might be negotiating for the electro-magnetic gun. We had found out where he was, in all probability, but we were powerless to help him. I thought of Miss Lowe, and picked up the receiver which Kennedy had dropped.

She did not answer. The wire had been cut. We were isolated!

Kennedy had jumped to the window. I followed to restrain him, fearing that he had some mad scheme for climbing out. Instead, quickly he placed a peculiar arrangement, from the little package he had brought, holding it to his eye as if sighting it, his right hand grasping a handle as one holds a stereoscope. A moment later, as I examined it more closely, I saw that instead of looking at anything he had before him a small parabolic mirror turned away from him.

His finger pressed alternately on a b.u.t.ton on the handle and I could see that there flashed in the little mirror a minute incandescent lamp which seemed to have a special filament arrangement.

The glaring sun was streaming in at the window and I wondered what could possibly be accomplished by the little light in compet.i.tion with the sun itself.

"Signaling by electric light in the daytime may sound to you ridiculous," explained Craig, still industriously flashing the light, "but this arrangement with Professor Donath's signal mirror makes it possible, all right.

"I hadn't expected this, but I thought I might want to communicate with Burke quickly. You see, I sight the lamp and then press the b.u.t.ton which causes the light in the mirror to flash. It seems a paradox that a light like this can be seen from a distance of even five miles and yet be invisible to one for whom it was not intended, but it is so. I use the ordinary Morse code--two seconds for a dot, six for a dash with a four-second interval."

"What message did you send?" I asked.

"I told him that Baron Kreiger was at five hundred and one East Fifth, probably; to get the secret service office in New York by wire and have them raid the place, then to come and rescue us. That was Annenberg. He must have come up by that trolley we heard pa.s.sing just before."

The minutes seemed ages as we waited for Burke to start the machinery of the raid and then come for us.

"No--you can't have a cigarette--and if I had a pair of bracelets with me, I'd search you myself," we heard a welcome voice growl outside the door a few minutes later. "Look in that other pocket, Tom."

The lock grated back and there stood Burke holding in a grip of steel the undersized Annenberg, while the chauffeur who had driven our car swung open the door.

"I'd have been up sooner," apologized Burke, giving the anarchist an extra twist just to let him know that he was at last in the hands of the law, "only I figured that this fellow couldn't have got far away in this G.o.d-forsaken Ducktown and I might as well pick him up while I had a chance. That's a great little instrument of yours, Kennedy. I got you, fine."