I went directly to our apartment after Craig left me and for a little while sat up, speculating on the probabilities of the case.

Senora de Moche had told us of her ancestor who had been intrusted with the engraved dagger, of how it had been handed down, of the death of her brother; she had told us of the murder of the ancestor of Inez Mendoza, of the curse of Mansiche. Was this, after all, but a reincarnation of the bloody history of the Gold of the Gods?

There were the shoe-prints in the mummy case. They were Lockwood's. How about them? Was he telling the truth? Now had come the poisoned cigarettes. All had followed the threats:

BEWARE THE CURSE OF MANSICHE ON THE GOLD OF THE GODS.

Several times I had been forced already to revise my theories of the case. At first I had felt that it pointed straight toward Lockwood. But did it seem to do so now?

Suppose Lockwood had stolen the dagger from the Museum, although he denied even that. Did that mean, necessarily that he committed the murder with it, that he now had it? Might he not have lost it? Might not some one else—the Senora, or Alfonso, or both—have obtained it? Might not Mendoza have been murdered with it by some other hand to obtain or to hide the secret on its bloody blade?

I went to bed, still thinking, no nearer a conclusion than before, prepared to dream over it.

That is the last I remember.

When I regained consciousness, I was lying on the bed still, but Craig was bending over me. He had just taken a rubber cap off my face, to which was attached a rubber tube that ran to a box perhaps as large as a suitcase, containing a pump of some kind.

I was too weak to notice these things right away, too weak to care much about them, or about anything else.

"Are you all right now, old man?" he asked, bending over me.

"Y-Yes," I gasped, clutching at the choking sensation in my throat.
"What has happened?"

Perhaps I had best tell it as though I were not the chief actor; for it came to me in such disjointed fragmentary form, that it was some time before I could piece it together.

Craig had seen Burke, and had found that everything was all right. Then he had made the few little investigations that he intended. But he had not been to the laboratory. There had been no light there that night.

At last when he arrived home, he had found a peculiar odour in the hall, but had thought nothing of it, until he opened our door. Then there rushed out such a burst of it that he had to retreat, almost fainting, choking and gasping for breath.

His first thought was for me; and protecting himself as best he could he struggled through to my room, to find me lying on the bed, motionless, almost cold.

He was by this time too weak to carry me. But he managed to reach the window and throw it wide open. As the draught cleared the air, he thought of the telephone and with barely strength enough left called up one of the gas companies and had a pulmotor sent over.

Now that the danger was past for me, and he felt all right, his active mind began at once on the reconstruction of what had happened.

What was it—man or devil? Could a human fly have scaled the walls, or an aeroplane have dropped an intruder at the window ledge? The lock on the door did not seem to have been tampered with. Nor was there any way by which entrance could have been gained from a fire escape. It was not illuminating gas. Every one agreed on that. No, it was not an accident. It was an attempt at murder. Some one was getting close to us. Every other weapon failing, this was desperation.

I had been made comfortable, and he was engaged in one of his characteristic searches, with more than ordinary eagerness, because this was his own apartment, and it was I who had been the victim.

I followed him languidly as he went over everything, the furniture, the walls, the windows, the carpets—there looking for finger-prints, there for some trace of the poisonous gas that had filled the room. But he did not have the air of one who was finding anything. I was too tired to reason. This was but another of the baffling mysteries that confronted us.

A low exclamation caused me to open my eyes and try to discover what was the cause. He was bending over the lock of the door looking at it intently.

"Broken?" I managed to say.

"No—corroded," he replied. "You keep still. Save your energy. I've got strength enough for two, for a while."

He came over to the bed and bent over me. "I won't hurt you," he encouraged, "but just let me get a drop of your blood."

He took a needle and ran it gently into my thumb beside the nail. A drop or two of blood oozed out and he soaked it up with a piece of sterile gauze.

"Try to sleep," he said finally.

"And you?" I asked.

"It's no use. I'm going over to the laboratory. I can't sleep. There's a cop down in front of the house. You're safe enough. By George, if this case goes much further we'll have half the force standing guard. Here—drink that."

I had made up my mind not to go to sleep, if he wouldn't, but I slipped up when I obeyed him that time. I thought it was a stimulant but it turned out to be a sedative.

I did not wake up until well along in the morning, but when I did I was surprised to find myself so well. Before any one could stop me, I was dressed and had reached the door.

A friend of ours who had volunteered to stay with me was dozing on a couch as I came out.

"Too late, Johnson," I called, trying hard to be gay, though I felt anything but like it. "Thank you, old man, for staying with me. But I'm afraid to stop. You're stronger than I am this morning—and besides you can run faster. I'm afraid you'll drag me back."

He did try to do it, but with a great effort of will-power I persuaded him to let me go. Out in the open air, too, it seemed to do me good. The policeman who had been stationed before the house gazed at me as though he saw a ghost, then grinned encouragingly.

Still, I was glad that the laboratory was only a few blocks away, for I was all in by the time I got there, and hadn't even energy enough to reply to Kennedy's scolding.

He was working over a microscope, while by his side stood in racks, innumerable test-tubes of various liquids. On the table before him lay the lock of our door which he had cut out after he gave me the sleeping draught.

"What was it?" I asked. "I feel as if I had been on a bust, without the recollection of a thing."

He shook his head as if to discourage conversation, without taking his eyes off the microscope through which he was squinting. His lips were moving as if he were counting. I waited in impatient silence until he seemed to have finished.

Then, still without a word, he took up a test-tube and dropped into it a little liquid from a bottle on a shelf above the table. His face lighted up, and he regarded the reaction attentively for some time. Then he turned to me, still holding the tube.

"You have been on a bust," he said with a smile as if the remark of a few minutes before were still fresh. "Only it was a laughing gas jag—nitrous oxide."

"Nitrous oxide?" I repeated. "How—what do you mean?"

"I mean simply that a test of your blood shows that you were poisoned by nitrous oxide gas. You remember the sample of blood which I squeezed from your thumb? I took it because I knew that a gas—and it has proved to be nitrous oxide—is absorbed through the lungs into the circulation and its presence can be told for a considerable period after administration."

He paused a moment, then went on: "To be specific in this case I found by microscopic examination that the number of corpuscles in your blood was vastly above the normal, something like between seven and eight million to a drop that should have had somewhat more than only half that number. You were poisoned by gas that—"

"Yes," I interrupted, "but how, with all the doors locked?"

"I was coming to that," he said quietly, picking up the lock and looking at it thoughtfully.

He had already placed it in a porcelain basin, and in this basin he had poured some liquids. Then he passed the liquids through a fine screen and at last took up a tube containing some of the resulting liquid.

"I have already satisfied myself," he explained, "but for your benefit, seeing that you're the chief sufferer, I'll run over a part of the test. You saw the reaction which showed the gas a moment ago. I have proved chemically as well as microscopically that it is present in your blood. Now if I take this test-tube of liquid derived from my treatment of the lock and then test it as you saw me do with the other, isn't that enough for you? See—it gives the same reaction."

It did, indeed, but my mind did not react with it.

"Nitrous oxide," he continued, "in contact with iron, leaves distinct traces of corrosion, discernible by chemical and microscopic tests quite as well as the marks it leaves in the human blood. Manifestly, if no one could have come in by the windows or doors, the gas must have been administered in some way without any one coming into the room. I found no traces of an intruder."

It was a tough one. Never much good at answering his conundrums when I was well, I could not even make a guess now.

"The key-hole, of course!" he explained. "I cut away the entire lock, and have submitted it to these tests which you see."

"I don't see it all yet," I said.

"Some one came to our door in the night, after gaining entrance to the hall—not a difficult thing to do, we know. That person found our door locked, knew it would be locked, knew that I always locked it. Knowing that such was the case, this person came prepared, bringing perhaps, a tank of compressed nitrous oxide, certainly the materials for making the gas expeditiously."

I began to understand how it had been done.

"Through the keyhole," he resumed, "a stream of the gas was injected. It soon rendered you unconscious, and that would have been all, if the person had been satisfied. A little bit would have been harmless enough. But the person was not satisfied. The intention was not to overcome, but to kill. The stream of gas was kept up until the room was full of it.

"Only my return saved you, for the gas was escaping very slowly. Even then, you had been under it so long that we had to resort to the wonderful little pulmotor after trying both the Sylvester and Schaefer methods and all other manual means to induce respiration. At any rate we managed to undo the work of this fiend."

I looked at him in surprise, I, who didn't think I had an enemy in the world.

"But who could it have been?" I asked.

"We are pretty close to that criminal," was the only reply he would give, "providing we do not spread the net in sight of the quarry."

"Why should he have wanted to get me?" I repeated.

"Don't flatter yourself," replied Craig. "He wanted me, too. There wasn't any light in the laboratory last night. There was a light in our apartment. What more natural than to think that we were both there? You were caught in the trap intended for both of us."

I looked at him, startled. Surely this was a most desperate criminal. To cover up one murder—perhaps two—he did not hesitate to attempt a third, a double murder. The attack had been really aimed at Kennedy. It had struck me alone. But it had miscarried and Craig had saved my life.

As I reflected bitterly, I had but one satisfaction. Wretched as I felt, I knew that it had spared Craig from slowing up on the case at just the time when he was needed.

The news of the attempt spread quickly, for it was a police case and got into the papers.

It was not half an hour after I reached the laboratory that the door was pushed open by Inez Mendoza, followed by a boy spilling with fruit and flowers like a cornucopia.

"I drove to the apartment," she cried, greatly excited and sympathetic, "but they told me you had gone out. Oh, I was glad to hear it. Then I knew it wasn't so serious. For, somehow, I feel guilty about it. It never would have happened if you hadn't met me."

"I'm sure it's worth more than it cost," I replied gallantly.

She turned toward Kennedy. "I'm positively frightened," she exclaimed. "First they direct their attacks against my father—then against me—now against you. What will it be next? Oh—it is that curse—it is that curse!"

"Never fear," encouraged Kennedy, "we'll get you out—we'll get all of us out, now, I should say. It's just because they are so desperate that we have these things. As long as there is nothing to fear a criminal will lie low. When he gets scared he does things. And it's when he does things that he begins to betray himself."

She shuddered. "I feel as though I was surrounded by enemies," she murmured. "It is as if an unseen evil power was watching over me all the time—and mocking me—striking down those I love and trust. Where will it end?"

Kennedy tried his best to soothe her, but it was evident that the attack on us could not have had more effect, if it had been levelled direct at her.

"Please, Senorita," he pleaded, "stand firm. We are going to win. Don't give in. The Mendozas are not the kind to stop defeated."

She looked at him, her eyes filled with tears.

"It was my father's way," she choked back her emotion. "How could you, a stranger, know?"

"I didn't know," returned Kennedy. "I gathered it from his face. It is also his daughter's way."

"Yes," she said, straightening up and the fire flashing from her eyes, "we are a proud, old, unbending race. Good-bye. I must not interrupt your work any longer. We are also a race that never forgets a friend."

A moment later she was gone.

"A wonderful woman," repeated Kennedy absently.

Then he turned again to his table of chemicals.

The telephone had begun to tinkle almost continuously by this time, as one after another of our friends called us up to know how we were getting on and be assured of our safety. In fact I didn't know that it was possible to resuscitate so many of them with a pulmotor.

"By George, I'm glad it wasn't any more serious," came Norton's voice from the doorway a moment later. "I didn't see a paper this morning. The curator of the Museum just told me. How did it happen?"

Kennedy tried to pass it off lightly, and I did the same, for as I was up longer I really did feel better.

Norton shook his head gravely, however.

"No," he said, "there were four of us got warnings. They are a desperate, revengeful people."

I looked at him quickly. Did he mean the de Moches?