Dr. Leslie looked at Haynes searchingly. "Who was it?" he asked. "Madame Dupres?"

Haynes did not hesitate. "Yes," he nodded. "I had an appointment with her and told her that if I was late it would probably be that I had stopped here."

The answer came so readily that I must confess that I was suspicious of it.

"Did Madame Dupres know the Baroness Von Dorf?" asked Craig quickly.

"Yes, indeed," returned Haynes, then stopped suddenly.

"But they didn't travel in the same circle, did they?" asked Dr. Leslie, with the air of the cross-examiner who wished to place on record a fact that might later prove damaging.

"Not exactly," answered Haynes, with some hesitation.

"You knew her, of course?" added Craig.

Haynes nodded.

"I wonder if you could locate the Baroness," pursued Kennedy.

Haynes seemed to express no surprise at the obvious implication that she was missing. "I have no objection to trying," he answered simply; then, with a glance at his watch, he reached for his hat and stick and excused himself. "I'm afraid I must go. If I can be of any assistance," he added, "don't hesitate to call on me. Delaney and I were pretty closely associated in this deal and I feel that nothing is too much to ask of me if it is possible to clear up the mystery of his death, if there is any."

He departed as quickly as he had come.

"I wonder what he dropped in for?" I remarked.

"Whatever it was, he didn't get it," returned Leslie.

"I'm not so sure of that," I said, remembering the brief telephone conversation with Madame Dupres.

Kennedy did not appear to be bothering much about the question one way or the other. He had let his cigar go out during Haynes' visit, but now that we were alone again he continued his minute search of the premises.

He opened a closet which evidently contained nothing but household utensils and was about to shut the door when an idea occurred to him. A moment later he pulled from the mystic depths an electric vacuum cleaner and dragged it over to the sun-parlor.

Without a word we watched him as he ran it over the floor and walls, even over the wicker stands on which the plants stood, and then over the floor coverings and furniture of the other rooms that opened into the conservatory. What he was after I could not imagine, but I knew it was useless to ask him until he had found it or had some reason for telling it.

Carefully he removed the dust and dirt from the machine and wrapped it up tightly in a package.

We parted from Dr. Leslie at the door of the apartment, promising to keep in touch with him and let him know the moment anything happened.

At the first telegraph office Kennedy entered and sent off a long message to our friend Burke of the Secret Service in Washington, asking him to locate the Baroness, if possible, in that city, and to give any information he might have about either Haynes or Madame Dupres.

"It's still early in the evening," remarked Kennedy as we left the telegraph office. "Suppose we drop around to the St. Quentin. Perhaps we may run into our friends there."

The St. Quentin was a favorite resort of foreigners in New York, and I, at least, entered prepared to suspect everyone.

"Not all these mysterious-looking men and women," laughed Kennedy, noticing me as we walked through the lobby, "are secret agents of foreign governments."

"Still they look as if they might give you the 'high sign,'" I replied, "particularly if you flashed a bankroll."

"I don't doubt it," he agreed, his eye roving over the throng. "I suspect that Scotland Yard and the Palais de Justice might be quite pleased to see some faces here rather than on the other side of the Atlantic."

He drew me into an angle and for some moments we studied the passing crowd of diplomats and near-diplomats.

A moment later I saw Kennedy bow and, following the direction of his eyes, looked up to a sort of mezzanine gallery. There were Haynes and a most attractive woman, talking earnestly.

"Madame Dupres," Craig whispered to me, aside.

She was tall, slender, gowned in the most modish manner, and had a foreign way about her that would have fascinated one even more cosmopolitan than a Texas veterinary.

Now and then someone would stop and chat with them and it seemed that they were on very good terms, at least with a certain group at the St. Quentin.

Kennedy moved out further into the lobby where he was more noticeable; then, with a sudden resolution, mounted the steps to the mezzanine floor and approached Haynes.

"Let me introduce Professor Kennedy, Madame Dupres," presented Haynes.

Kennedy bowed.

Whatever one's opinion of madame, he was forced to admit that she was clever. It was evident, also, that she and Haynes were on very intimate terms, also.

"I hope that you will be able to clear up the mystery that the newspapers have found in Mr. Delaney's death," she remarked. "Mr. Haynes has told me that he met you tonight with Dr. Leslie. By the way, has he told you his own theory?" she asked.

"We shall do our best," replied Kennedy, meeting her eye in as impersonal a manner as it was possible, for it is always difficult to dissociate a beautiful woman from a case like this and judge her not as a beautiful woman but on the merits of the case. "No, Mr. Haynes has not told me his theory—yet."

"I'm very glad to have met you," she added, extending her daintily gloved hand to Kennedy, "and you may be sure that if there is any way in which I can be of service I shall expect you to call on me. Just now I hope you will excuse me. I have some letters to get off—and I will leave you men to discuss Mr. Haynes' theory without being hampered by a mere woman. Never mind, Harris," she added as Haynes made as if to escort her to the ladies' writing room.

As Madame Dupres passed down the steps there was no denying that she made a splendid impression. Haynes watched her with a glance that was almost ravenous. There could be no doubt of her influence over him.

As she passed through the lobby she paused at the telegraph desk a moment, then went into the writing room.

"Yes, I think I have an explanation," began Haynes, when she was out of sight. "I've been trying to figure out what could have killed Delaney. Of course I can only guess, but I don't think it is such a bad guess."

"What is it?" asked Craig.

"You remember the mercury vapor light?"

Kennedy nodded.

"Mercury vapor lights of that sort are a pretty good source of ultra-violet rays sometimes," went on Haynes. "Well, doubtless you know that various plants belonging to different families produce free prussic acid. They are really cyanogenetic plants. Light and the assimilation processes depending on light exert a favorable influence on cyanogenesis. For instance, a mixture of citric acid with a much smaller amount of potassium nitrite and a trace of bicarbonate of iron, if exposed to light, will generate hydrocyanic acid. That, I believe, is what actually happens in some plant tissues. Animals rarely touch such plants. I believe that such a process might be aided rather than retarded by ultra-violet rays. What do you think of it?"

Craig was following Dr. Haynes keenly. As for me, I was astounded by his frankness. I recalled what Kennedy had already said up in Delaney's apartment, and watched his face covertly.

"Your explanation is plausible," was all that Craig said. "By the way, have you found out anything about the Baroness?"

"Not a word, yet," replied Haynes unhesitatingly. "She seems to be out of town."

"And madame—has she any idea where she is?"

Haynes shook his head. "You may rest assured," replied Haynes in a tone that was meant to carry conviction, "that if we can find out we shall be only too happy to do so—ourselves."

There was nothing to be gained by further inquiry here, and I could imagine that Kennedy was burning with anxiety to get at work on his own line of inquiry at the laboratory. After a few minutes of conversation we excused ourselves and left the hotel.

Craig's air of abstraction was not such as to invite further questioning, and I left him an hour or so later in the laboratory surrounded by his microscopes, slides, and innumerable test-tubes which he had prepared for some exceedingly minute investigation in which his exact soul delighted.

How late he worked I do not know, for I did not hear him come into our apartment. But he was up very early, in fact woke me up stirring around the living room.

I had scarcely completed dressing, while he scanned the morning papers in a vain hope that some stray news item might shed some light on the mystery in which we were now involved, when the whirr of our door buzzer announced that we had an unusually early caller.

Kennedy opened the door and admitted a stranger. He was one of those well-groomed middle-aged men whose appearance denotes with what care they seek by every means to retain youth that is fast passing. I could imagine him calmly calculating even his vices.

"My name is Ames—Ashby Ames," he introduced. "Dr. Leslie, the coroner, has suggested that I see you."

Ames looked as if he had been traveling all night and had not had a chance to freshen himself up in his haste.

"I've just heard about that trouble down at my apartment," he continued, "and, though I had planned a trip for my health to the southern resorts, I thought it best for me to come right back to New York. It's a beastly mess."

He had thrown his hat vindictively on the table, though his manner to us was rather that of one seeking advice. "Why," he stormed, "this affair is the limit! I rent my apartment to an apparently reputable person. And what do I find? It is not even a mere scandal. It is worse. The place is closed and guarded—quarantined, as it were. I can't get back into my own rooms!"

Kennedy smiled. "I can't blame you for feeling vexed, Mr. Ames," he soothed, "but I'm sure I don't know what I can do for you more than I am doing. We are making every effort to clear the thing up—and I have been on the case, you must remember, less than twelve hours."

"Oh, I've no criticism of you," rejoined Ames, somewhat mollified. "I didn't come here to criticise. I came only because I thought you might like to know that I was back in town, and because Dr. Leslie mentioned your name. No, indeed—no criticism. Only," he added, "now that my vacation is spoiled and I am back in town, there is going to be some action—that's all."

"It can't come too swiftly for me," encouraged Craig.

"I'm going to jump right into this beastly row," pursued Ames aggressively. "This morning I'm going to look these people up. They tell me that Baroness has been spending a good deal of time at my place. Pine business—eh? She's disappeared. But I'll get after that Haynes and the Madame Dupres they tell me about—and I'll let you know if I find out anything."

He had not given Kennedy a chance to say anything, and in fact Kennedy did not seem to want to say anything yet.

"Just thought I'd drop in," concluded Ames, who hadn't taken a chair, but now extended his hand to us; "I think I'll drop into a Turkish bath and freshen up a bit. Keep in touch with me."

We shook hands and Ames departed, bustling out as he had bustled in.

Kennedy looked at me and laughed as the door closed. "If we have many more people co-operating with us," he exclaimed, "we may resign and let this case solve itself."

"I don't think that is likely," I replied.

"Not unless we hear from Burke," he agreed. "There is plenty for me to do in the laboratory—but I do wish Burke would wire."

The morning passed, and still there was no word from Burke.

"I think we might drop around to the St. Quentin for lunch," suggested Kennedy in the forenoon. "We might pick up some news there."

We had scarcely entered when we met Haynes pacing up and down the lobby furiously.

"What's the matter?" inquired Craig, eyeing him searchingly.

"Why," he replied nervously, sticking his thumbs into his waistcoat pockets and then plunging them into his trousers pockets as if it was with the utmost difficulty he controlled those unruly members from doing violence to somebody, "that fellow Ames from whom Delaney hired the apartment had just returned suddenly to town. I saw him talking to Madame Dupres in the hotel parlor. She seemed a bit nervous, so I went in to speak to her. But she said everything was all right and that she'd meet me out here in a few minutes. It's quarter of an hour now. I think he's threatening her with something."

Haynes was evidently worried. I wondered whether he was afraid that Ames might worm from her some secret common to the two, for I did not doubt that Ames was a clever and subtle attorney and capable of obtaining a great deal of information by his kind of kid-glove third degree.

"I should like to see both of them," decided Craig quickly.

Before Haynes could say anything more, he strode into the hotel parlor. Haynes and I followed a short distance behind.

There was an air of tense, suppressed excitement in the group, but of all of us, I felt that Madame Dupres was the coolest.

"I see you've lost no time in getting busy," nodded Craig to Ames.

"No," he replied easily. "This is certainly a very interesting situation which madame here has just outlined to me."

Haynes came up just in time to catch the last words.

"I say, Ames," he almost roared, "you may be a clever lawyer, but you must remember that you are also expected to be a gentleman. There are limits to questioning a woman when she has not the advantage of having a friend to advise her."

For a moment I thought there was going to be a fight, but Kennedy moved unobtrusively between the two men. As for Madame Dupres, I felt that really she was a match for both of them.

Instead of getting mad, however, Ames merely laughed.

"Why, Haynes," he said quietly, "I don't think you ought to complain. I understand that you, now representing Delaney's Texas syndicate, have already signed the final contract for the deal with those whom Madame Dupres represents and have received a certified check from them as a first payment to bind the bargain."

Haynes turned almost livid, then recovering himself, glanced at Madame Dupres.

"Why, Harris, I didn't think there was any secrecy about it now," she said, seeing the change in him. "If there is, I'm sorry."

"There isn't," replied Haynes, quickly recovering his composure. "Only I just didn't like to see a lawyer, an outsider, quizzing you, that's all."

Jealousy was stamped in every line of Haynes' face. Ames said nothing, but it was impossible to escape the look of gratification which he shot at Kennedy as he brought out the startling new development.

Madame Dupres was clever enough to see that no good could come of prolonging an interview for which now there was an excuse to break up.

"Take me in to lunch, Harris," she said, slipping her arm familiarly into his. "Good-morning, gentlemen."

Somehow I felt that she would have liked to add, "And if you see the Baroness, tell her I have beaten her to it."

Ames watched them depart with an air of cynical satisfaction, paused a moment, then in turn excused himself from us.

What did it mean? What was behind all this intrigue. Was it merely to get this cattle contract, big as that was?

We lunched together at the St. Quentin, and it was evident that Madame Dupres was doing her best to smooth over the ruffled feelings of her lover.

Luncheon over, Kennedy plunged with redoubled energy into his laboratory investigation. He said little, but I could tell from his manner that he had found something that was very fascinating to him.