"A woman?" I queried, in surprise. "A j.a.p, too?"

"No, a white woman, rather good-looking, too, with dark hair and eyes.

She seemed to be waiting for him. Afterward I made inquiries. She has been seen about there before."

"Who was she?" I asked, fancying perhaps Miss Langdale had made another visit while she was out, although from the time it did not seem possible.

"I followed her to her house. Her name is Hackstaff--"

"The first trained nurse!" I exclaimed.

"Miss Hackstaff is an enigma," confessed Kennedy. "At first I thought that perhaps she might be one of those women whom the Oriental type fascinated, that she and Kato might be plotting. Then I have considered that perhaps her visits to Kato may be merely to get information--that she may have an ax to grind. Both Kato and she will bear watching, and I have made arrangements to have it done. I've called on that young detective, Chase, whom I've often used for the routine work of shadowing. There's nothing more that we can do now until to-morrow, so we might as well turn in."

Early the next day Kennedy was again at work, both in his own laboratory and in that of the Health Department, making further studies of the food and the effect it had on the pigeons, as well as observing what changes were produced by the white tablets he had extracted from the yeast.

It was early in the forenoon when the buzzer on the laboratory door sounded and I opened the door to admit Chase in a high state of excitement.

"What has happened?" asked Craig, eagerly.

"Many things," reported the young detective, breathlessly. "To begin with, I followed Miss Hackstaff from her apartment this morning. She seemed to be worked up over something--perhaps had had a sleepless night. As nearly as I could make out she was going about aimlessly.

Finally, however, I found that she was getting into the neighborhood of Doctor Aitken and of the Forum. Well, when we got to the Forum she stopped and waited in front of it--oh, I should say almost half an hour. I couldn't make out what it was she wanted, but at last I found out."

He paused a moment, then raced on, without urging. "Miss Langdale came out--and you should have seen the Hackstaff woman go for her." He drew in his breath sharply at the reminiscence. "I thought there was going to be a murder done--on Riverside Drive. Miss Langdale screamed and ran back into the apartment. There was a good deal of confusion. The hall-boys came to the rescue. In the excitement, I managed to slip into the elevator with her. No one seemed to think it strange then that an outsider should be interested. I went up with her--saw Wardlaw, as she poured out the story. He's a queer one. Is he RIGHT?"

"Why?" asked Craig, indulgently.

"He seems so nervous; things upset him so easily. Yet, after we had taken care of Miss Langdale and matters had quieted down, I thought I might get some idea of the cause of the fracas and asked him if he knew of any reason. Why, he looked at me kind of blankly, and I swear he acted as though he had almost forgotten it already. I tell you, he's not RIGHT."

Remembering our own experience, I glanced significantly at Craig.

"Korsakoff's syndrome?" I queried, laconically. "Another example of a mind confused even on recent events?"

Kennedy, however, was more interested in Chase. "What did Miss Hackstaff do?" he asked.

"I don't know. I missed her. When I got out again she was gone."

"Pick her up again," directed Craig. "Perhaps you'll get her at her place. And see, this time, if you can get what I asked you."

"I'll try," returned Chase, much pleased at the words of commendation which Craig added as he left us again.

On what errand Chase had gone I could not guess, except that it had something to do with this strange woman who had so unexpectedly entered the case. Nor was Craig any more communicative. There were evidently many problems which only events could clear up even in his mind. Though he did not say anything, I knew that he was as impatient as I was, and as Leslie, too, who called up once or twice to learn whether he had discovered anything. There was nothing to do but wait.

It was early in the afternoon that the telephone rang and I answered it. It was Chase calling Kennedy. I heard only half the conversation and there was not much of that, but I knew that something was about to happen. Craig hastily summoned a cab, then in rapid succession called up Doctor Aitken and Leslie, for whom we stopped as our driver shot us over to the Forum Apartments.

There was no ceremony or unnecessary explanation about our presence, as Kennedy entered and directed Miss Langdale to bring her patients into the little office-study of Doctor Wardlaw.

Miss Langdale obeyed reluctantly. When she returned I felt that it was appreciable that a change had taken place. Mrs. Wardlaw, at least, was improved. She was still ill, but she seemed to take a more lively interest in what was going on about her. As for Doctor Wardlaw, however, I could not see that there had been any improvement in him.

His nervousness had not abated. Kato, whom Kennedy summoned at the same time, preserved his usual imperturbable exterior. Miss Langdale, in spite of the incident of the morning, was quite as solicitous as ever of her charges.

We had not long to wait for Doctor Aitken. He arrived, inquiring anxiously what had happened, although Kennedy gave none of us any satisfaction immediately as to the cause of his quick action. Aitken fidgeted uneasily, glancing from Kennedy to Leslie, then to Miss Langdale, and back to Kennedy, without reading any explanation in the faces. I knew that Craig was secretly taking his time both for its effect on those present and to give Chase a chance.

"Our poisons and our drugs," he began, leisurely, at length, "are in many instances the close relatives of harmless compounds that represent the intermediate steps in the daily process of metabolism. There is much that I might say about protein poisons. However, that is not exactly what I want to talk about--at least first."

He stopped to make sure that he had the attention of us all. As a matter of fact, his manner was such that he attracted even the vagrant interest of the Wardlaws.

"I do not know how much of his suspicions Commissioner Leslie has communicated to you," he resumed, "but I believe that you have all heard of the disease beriberi so common in the Far East and known to the j.a.panese as kakke. It is a form of polyneuritis and, as you doubtless know, is now known to be caused, at least in the Orient, by the removal of the pericarp in the polishing of rice. Our milling of flour is, in a minor degree, a.n.a.logous. To be brief, the disease arises from the lack in diet of certain substances or bodies which modern scientists call vitamines. Small quant.i.ties of these vital principles are absolutely essential to normal growth and health and even to life itself. They are nitrogenous compounds and their absence gives rise to a cla.s.s of serious disorders in which the muscles surrender their store of nitrogen first. The nerves seems to be the preferred creditors, so to speak. They are affected only after the muscles begin to waste. It is an abstruse subject and it is not necessary for me to go deeper into it now."

I controlled my own interest in order to watch those about me. Kato, for one, was listening attentively, I saw.

"In my studies of the diet of this household," continued Kennedy, "I have found that substances have been used in preparing food which kill vitamines. In short, the food has been denatured. Valuable elements, necessary elements, have been taken away."

"I, sir, not always in kitchen, sir," interrupted Kato, still deferential. "I not always know--"

With a peremptory wave of his hand Kennedy silenced the j.a.p.

"It has long been a question," he hurried on, "whether these vitamines are tangible bodies or just special arrangements of molecules. Recently government investigators have discovered that they are bodies that can be isolated by a special process from the filtrate of brewer's yeast by Lloyd's reagent. Five grams of this"--he held up some of the tablets he had made--"for a sixty-kilogram person each day are sufficient. Unknown to you, I have introduced some of this substance into the food already deficient in vitamines. I fancy that even now I can detect a change,"

he nodded toward Mrs. Wardlaw.

There was a murmur of surprise in the room, but before Craig could continue further the door opened and Mrs. Wardlaw uttered a nervous exclamation. There stood Chase with a woman. I recognized her immediately from Kennedy's description as Miss Hackstaff.

Chase walked deliberately over to Kennedy and handed him something, while the nurse glanced calmly, almost with pity, at Mrs. Wardlaw, ignoring Wardlaw, then fixing her gaze venomously on Miss Langdale.

Recalling the incident of the morning, I was ready to prevent, if necessary, a repet.i.tion now. Neither moved. But it was a thrilling, if silent, drama as the two women glared at each other.

Kennedy was hastily comparing the anonymous note he had received with something Chase had brought.

"Some one," he shot out, suddenly, looking up and facing us, "has, as I have intimated, been removing or destroying the vital principle in the food--these vitamines. Clearly the purpose was to make this case look like an epidemic of beriberi, polyneuritis. That part has been clear to me for some time. It has been the source of this devilish plot which has been obscure. Just a moment, Kato, I will do the talking. My detective, Chase, has been doing some shadowing for me, as well as some turning over of past history. He has found a woman, a nurse, more than a nurse, a secret lover, cast off in favor of another. Miss Hackstaff--you wrote that letter--it is your hand--for revenge--on Miss Langdale and--"

"You shan't have him!" almost hissed Helen Hackstaff. "If I cannot--no one shall!"

Natalie Langdale faced her, defiant. "You are a jealous, suspicious person," she cried. "Doctor Aitken knows--"

"One moment," interrupted Craig. "Mrs. Marbury is gone. Mrs. Wardlaw is weakened. Yet all who are affected with nerve troubles are not necessarily suffering from polyneuritis. Some one here has been dilettanting with death. It is of no use," he thundered, turning suddenly on a cowering figure. "You stood to win most, with the money and your unholy love. But Miss Hackstaff, cast off, has proved your Nemesis. Your nervousness is the nervousness not of polyneuritis, but of guilt, Doctor Wardlaw!"

IX

THE RUBBER DAGGER

"Hypnotism can't begin to accomplish what Karatoff claims. He's a fake, Kennedy, a fake."

Professor Leslie Gaines of the Department of Experimental Psychology at the university paced excitedly up and down Craig's laboratory.

"There have been complaints to the County Medical Society," he went on, without stopping, "and they have taken the case up and arranged a demonstration for this afternoon. I've been delegated to attend it and report."

I fancied from his tone and manner that there was just a bit more than professional excitement involved. We did not know Gaines intimately, though of course Kennedy knew of him and he of Kennedy. Some years before, I recollected, he had married Miss Edith Ashmore, whose family was quite prominent socially, and the marriage had attracted a great deal of attention at the time, for she had been a student in one of his courses when he was only an a.s.sistant professor.

"Who is Karatoff, anyhow?" asked Kennedy. "What is known about him?"