It was not until after dinner that we heard again from Norton. He had evidently spent the time faithfully hanging about the Prince Edward Albert, but Whitney had not come in, although the Senora and Alfonso were about.

"I saw them leaving the dining-room," he reported to us in the laboratory directly afterward, "just as Whitney came in. They could not see me. I took good care of that. But, say, there is a change in Whitney, isn't there? I wonder what caused it?"

"It's as noticeable as that?" asked Kennedy. "And did she notice it?"

"I'm sure of it," replied Norton confidently. "She couldn't help it. Besides, after he left her and went into the dining-room himself she and Alfonso seemed to be discussing something. I'm sure it was that."

Kennedy said nothing, except to thank Norton and compliment him on his powers of observation. Norton took the praise with evident satisfaction, and after a moment excused himself, saying that he had some work to do over in the Museum.

He had no sooner gone than Kennedy took from a drawer a little packet of powder and an atomizer full of liquid, which he dropped into his pocket.

"I think the Prince Edward Albert will be the scene of our operations, to-night, Walter," he announced, reaching for his hat.

He seemed to be in a hurry and it was not many minutes before we entered. As he passed the dining-room he glanced in. There was Whitney, not half through a leisurely dinner. Neither of the de Moches seemed to be downstairs.

Kennedy sauntered over to the desk and looked over the register. We already knew that Whitney and the Senora had suites on the eighth floor, on opposite sides and at opposite ends of the hall. The de Moche suite was under the number 810. That of Whitney was 825.

"Is either 823 or 827 vacant?" asked Kennedy as the clerk came over to us.

He turned to look over his list. "Yes, 827 is vacant," he found.

"I'd like to have it," said Kennedy, making some excuse about our luggage being delayed, as he paid for it for the night.

"Front!" called the clerk, and a moment later we found ourselves in the elevator riding up.

The halls were deserted at that time in the evening except for a belated theatre-goer, and in a few minutes there would ensue a period in which there was likely to be no one about.

We entered the room next to Whitney's without being observed by any one of whom we cared. The boy left us, and it was a simple matter after that to open a rather heavy door that communicated between the two suites and was not protected by a Yale lock.

Instead of switching on the lights, Kennedy first looked about carefully until he was assured that there was no one there. It seemed to me to be an unnecessary caution, for we knew Whitney was down-stairs and would probably be there a long time. But he seemed to think it necessary. Positive that we were alone, he made a hasty survey of the rooms. Then he seemed to select as a starting-point a table in one corner of the sitting-room on which lay a humidor and a heavy metal box for cigarettes.

Quickly he sprinkled on the floor, from the hall door to the table on which the case of cigarettes lay, some of the powder which I had seen him wrap up in the laboratory before we left. Then, with the atomizer, he sprayed over it something that had a pungent, familiar odour—walking backwards from the hall door to the table, as he sprayed.

"Don't you want more light?" I asked, starting to cross to a window to let the moonlight stream in.

"Don't walk on it, Walter," he whispered, pushing me back. "No, I don't need any more light."

"What are you doing?" I asked, mystified at his actions.

"First I sprinkled some powdered iodine on the floor," he replied, "and then sprayed over just enough ammonia to moisten it. It will evaporate quickly, leaving what I call my anti-burglar powder."

"I'm sure I wouldn't be thought one of the fraternity for the world," I observed, stepping aside to give him all the room he wanted in which to operate.

He had finished his work by this time and now the evening wind was blowing away the slight fumes that had arisen. For a few moments he left our door into Whitney's room open, in order to insure clearing away the odour. Then he quietly closed it, but did not lock it again.

We waited a few minutes, then Craig leaned over to me. "I wish you'd go down and see how near Whitney is through dinner," he said. "If he is through, do something, anything to keep him down there. Only be as careful as you can not to be seen by any one who knows us."

I rode down in an empty elevator and cautiously made my way to the dining-room. Whitney had finished much sooner than I had expected and was not there. Much as I wanted not to be seen, I found that it was necessary to make a tour of the hotel to find him and I did so, wondering what expedient I would adopt to keep him down there if I found him. I did not have to adopt any, however. Whitney was almost alone in the writing-room, and a big pile of letters beside him showed me that he would be busy for some time. I rode back to the room to tell Craig, flattering myself that I had not been seen.

"Good," he exclaimed. "I don't think we'll have to wait much longer, if anything at all is going to happen."

In the darkness we settled ourselves for another vigil that was to last we knew not how long. Neither of us spoke as we half crouched in the shadow of our room, listening.

Slowly the time passed. Would any one take advantage of the opportunity to tamper with the box of cigarettes on the table?

I fell to speculating. Who could it possibly have been that had conceived this devilish plot? What was back of it all? I wondered whether it were possible that Lockwood, now that Mendoza was out of the way, could desire to remove Whitney, the sole remaining impediment to possessing the whole of the treasure as well as Inez? Then there were the Senora and Alfonso, the one with a deep race and family grievance, the other a rejected suitor. What might not they do with some weird South American poison?

Once or twice we heard the elevator door clang and waited expectantly, but nothing happened. I began to wonder whether, even if some one had a pass-key to the suite, we could hear him enter if he was quiet. The outside hall was thickly carpeted, and deadened every footfall if one exercised only reasonable care. The rooms themselves were much the same.

"Don't you think we might have the door ajar a little?" I suggested anxiously.

"Sh!" was Kennedy's only comment in the negative.

I glanced now and then at my watch and by straining my eyes was surprised to see how early it was yet. The minutes were surely leaden-footed.

In the darkness, I fell again to reviewing the weird succession of events. I am not by nature superstitious, but in the black silence I could well imagine a staring succession of eyes, beginning with the dilated pupils of Whitney and passing on to the corpse-like expression of Mendoza, but always ending with the remarkable, piercing, black eyes of the Indian woman with the melancholy-visaged son, as they had impressed me the first time I saw them and, in fact, ever since. Was it a freak of my mind, or was there some reason for it?

Suddenly I heard in the next room what sounded like a series of little explosions, as though some one were treading on match heads.

"My burglar powder works," muttered Craig to me in a hoarse whisper.
"Every step, even those of a mouse running across, sets it off!"

He rose quickly and threw open the door into Whitney's suite. I sprang after him.

There, in the shadows, I saw a dark form, starting back in quick retreat. But we were too late. He was cat-like, too quick for us.

In the dim light of the little explosions we could catch a glimpse of the person who had been craftily working with the dread drug to drive Whitney and others insane. But the face was masked!

He banged shut the door after him and fled down the hall, making a turn to a flight of steps.

We followed, and at the steps paused a moment. "You go up, Walter," shouted Kennedy. "I'll go down."

It was fifteen minutes later before we met downstairs, neither of us with a trace of the intruder. He seemed to have vanished like smoke.

"Must have had a room, like ourselves," remarked Craig somewhat chagrined at the outcome of his scheme. "And if he was clever enough to have a room, he is clever enough to have a disguise that would fool the elevator boys for a minute. No, he has gone. But I'll wager he won't try any more substitutions of stramonium-poisoned cigarettes for a while. It was too close to be comfortable."

We were baffled again, and this time by a mysterious masked man. Could it be the same whom we heard over the vocaphone addressed as "Doc"? Perhaps it was, but that gave us no hint as to his identity. He seemed just as far away as ever.

We waited around the elevators for some time, but nothing happened. Kennedy even sought out the manager of the hotel, and after telling who he was, had a search made of the guests who might be suspected. The best we could do was to leave word that the employees might be put on the lookout for anything of a suspicious nature.

Whitney, the innocent cause of all this commotion, was still in the writing-room with his letters.

"I think I ought to tell him," decided Kennedy as we passed down the lobby.

He seemed surprised to see us, as we strolled up to his writing desk, but pushed aside the few letters which he had not finished and asked us to sit down.

"I don't know whether you have noticed it," began Craig, "but I wonder how you feel?"

Whitney had expected something else rather than his health as the subject of a quiz. "Pretty good now," he answered before he knew it, "although I must admit that for the past few days I have wondered whether I wasn't slowing up a bit—or rather going too fast."

"Would you like to know why you feel that way?" asked Craig.

Whitney was now genuinely puzzled. It was perfectly evident, as it had been all the time, that he had not the slightest inkling of what was going on.

As Craig briefly unfolded what we had discovered and the reason for it,
Whitney watched him aghast.

"Poisoned cigarettes," he repeated slowly. "Well, who would ever have thought it. You can bet your last jitney I'll be careful what I smoke in the future, if I have to smoke only original packages. And it was that, partly, that ailed Mendoza?"

Kennedy nodded. "Don't take any pilocarpine, just because I told you that was what I used. You have given yourself the best prescription, just now. Be careful what you smoke. And, don't get excited if you seem to be stepping on matches up there in your room for a little while, either. It's nothing."

Whitney's only known way of thanking anybody was to invite them to adjourn to the cafe, and accordingly we started across the hall, after he had gathered up his correspondence. The information had made more work that night impossible for him.

As we crossed from the writing-room, we saw Alfonso de Moche coming in from the street. He saw us and came over to speak. Was it a coincidence, or was it merely a blind? Was he the one who had got away and now calculated to come back and throw us off guard?

Whitney asked him where he had been, but he replied quickly that his mother had not been feeling very well after dinner and had gone to bed, while he strolled out and had dropped into a picture show. That, I felt, was at least clever. The intruder had been a man.

De Moche excused himself, and we continued our walk to the cafe, where
Whitney restored his shattered peace of mind somewhat.

"What's the result of your detective work on Norton?" ventured Kennedy at last, seeing that Whitney was in a more expansive frame of mind, and taking a chance.

"Oh," returned Whitney, "he's scared, all right. Why, he has been hanging around this hotel—watching me. He thinks I don't know it, I suppose, but I do."

Kennedy and I exchanged glances.

"But he's slippery," went on Whitney. "He knows that he is being shadowed and the men tell me that they lose him, now and then. To tell the truth I don't trust most of these private detectives. I think their little tissue paper reports are half-faked, anyhow."

He seemed to want to say no more on the subject, from which I took it that he had discovered nothing of importance.

"One thing, though," he recollected, after a moment. "He has been going to see Inez Mendoza, they tell me."

"Yes?" queried Kennedy.

"Confound him. He pretty nearly got Lockwood in bad with her, too," said Whitney, then leaning over confidentially added, "Say, Kennedy, honestly, now, you don't believe that shoe-print stuff, do you?"

"I see no reason to doubt it," returned Kennedy with diplomatic firmness. "Why?"

"Well," continued Whitney, still confidential, "we haven't got the dagger—that's all. There—I never actually asserted that before, though I've given every one to understand that our plans are based on something more than hot-air. We haven't got it, and we never had it."

"Then who has it?" asked Kennedy colourlessly.

Whitney shook his head. "I don't know," he said merely.

"And these attacks on you—this cigarette business—how do you explain that," asked Craig, "if you haven't the dagger?"

"Jealousy, pure jealousy," replied Whitney quickly. "They are so afraid that we will find the treasure. That's my dope."

"Who is afraid?"

"That's a serious matter," he evaded. "I wouldn't say anything that I couldn't back up in a case of that kind. I'd get into trouble."

There was nothing to be gained by prolonging the conversation and
Kennedy made a move as though to go.

"Just give us a square deal," said Whitney as we left. "That's all we want—a square deal."

Kennedy and I walked out of the Prince Edward Albert and turned down the block.

"Well, have you found out anything more?" asked a voice in the shadow beside us.

We turned. It was Norton.

"I saw you talking to Whitney in the writing-room," he said, with a laugh, "then in the cafe, and I saw Alfonso come in. He still has those shadows on me. I wouldn't be surprised if there was one of them around in a doorway, now."

"No," returned Kennedy, "he didn't say anything that was important.
They still say they haven't the dagger."

"Of course," said Norton.

"You'll wait around a little longer?" asked Kennedy as we came to a corner and stopped.

"I think so," returned Norton. "I'll keep you posted."

Kennedy and I walked on a bit.

"I'm going around to see how Burke, O'Connor's man, is getting on watching the Mendoza apartment, Walter," he said at length. "Then I have two or three other little outside matters to attend to. You look tired. Why don't you go home and take a rest? I shan't be working in the laboratory to-night, either."

"I think I will," I agreed, for the strain of the case was beginning to tell on me.