We reached the Blake mansion and were promptly admitted. Miss Betty, bearing up bravely under Reginald's reassurances, greeted us before we were fairly inside the door, though she and her brother were not able to conceal the fact that their mother was no better. Miss Sears was out, for an airing, and the new nurse, Miss Rogers, was in charge of the patient.

"How do you feel, this morning?" inquired Kennedy as we entered the sun-parlor, where Mrs. Blake had first received us.

A single glance was enough to satisfy me of the seriousness of her condition. She seemed to be in almost a stupor from which she roused herself only with difficulty. It was as if some overpowering toxin were gradually undermining her already weakened constitution.

She nodded recognition, but nothing further.

Kennedy had set the dog basket down near her wheel-chair and she caught sight of it.

"Buster?" she murmured, raising her eyes. "Is—he—all right?"

For answer, Craig simply raised the lid of the basket. Buster already seemed to have recognized the voice of his mistress, and, with an almost human instinct, to realize that though he himself was still weak and ill, she needed encouragement.

As Mrs. Blake stretched out her slender hand, drawn with pain, to his silky head, he gave a little yelp of delight and his little red tongue eagerly caressed her hand.

It was as though the two understood each other. Although Mrs. Blake, as yet, had no more idea what had happened to her pet, she seemed to feel by some subtle means of thought transference that the intelligent little animal was conveying to her a message of hope. The caress, the sharp, joyous yelp, and the happy wagging of the bushy tail seemed to brighten her up, at least for the moment, almost as if she had received a new impetus.

"Buster!" she exclaimed, overjoyed to get her pet back again in so much improved condition.

"I wouldn't exert myself too much, Mrs. Blake," cautioned Kennedy.

"Were—were there any germs in the letter?" she asked, as Reginald and Betty stood on the other side of the chair, much encouraged, apparently, at this show of throwing off the lethargy that had seized her.

"Yes, but about as harmless as those would be on a piece of cheese,"
Kennedy hastened. "But I—I feel so weak, so played out—and my head—"

Her voice trailed off, a too evident reminder that her improvement had been only momentary and prompted by the excitement of our arrival.

Betty bent down solicitously and made her more comfortable as only one woman can make another. Kennedy, meanwhile, had been talking to Miss Rogers, and I could see that he was secretly taking her measure.

"Has Dr. Wilson been here this morning?" I heard him ask.

"Not yet," she replied. "But we expect her soon."

"Professor Kennedy?" announced a servant.

"Yes?" answered Craig.

"There is someone on the telephone who wants to speak to you. He said he had called the laboratory first and that they told him to call you here."

Kennedy hurried after the servant, while Betty and Reginald joined me, waiting, for we seemed to feel that something was about to happen.

"One of the unofficial detectives has unearthed a clue," he whispered to me a few moments later when he returned. "It was Garwood." Then to the others he added, "A car, repainted, and with the number changed, but otherwise answering the description of Dr. Wilson's has been traced to the West Side. It is somewhere in the neighborhood of a saloon and garage where drivers of taxicabs hang out. Reginald, I wish you would come along with us."

To Betty's unspoken question Craig hastened to add, "I don't think there is any immediate danger. If there is any change—let me know. I shall call up soon. And meanwhile," he lowered his voice to impress the instruction on her, "don't leave your mother for a moment—not for a moment," he emphasized.

Reginald was ready and together we three set off to meet Garwood at a subway station near the point where the car had been reported. We had scarcely closed the front door, when we ran into Duncan Baldwin, coming down the street, evidently bent on inquiring how Mrs. Blake and Betty were.

"Much better," reassured Kennedy. "Come on, Baldwin. We can't have too many on whom we can rely on an expedition like this."

"Like what?" he asked, evidently not comprehending.

"There's a clue, they think, to that car of Dr. Wilson's," hastily explained Reginald, linking his arm into that of his friend and falling in behind us, as Craig hurried ahead.

It did not take long to reach the subway, and as we waited for the train, Craig remarked: "This is a pretty good example of how the automobile is becoming one of the most dangerous of criminal weapons. All one has to do nowadays, apparently, after committing a crime, is to jump into a waiting car and breeze away, safe."

We met Garwood and under his guidance picked our way westward from the better known streets in the heart of the city, to a section that was anything but prepossessing.

The place which Garwood sought was a typical Raines Law hotel on a corner, with a saloon on the first floor, and apparently the requisite number of rooms above to give it a legal license.

We had separated a little so that we would not attract undue attention. Kennedy and I entered the swinging doors boldly, while the others continued across to the other corner to wait with Garwood and take in the situation. It was a strange expedition and Reginald was fidgeting while Duncan seemed nervous.

Among the group of chauffeurs lounging at the bar and in the back room anyone who had ever had any dealings with the gangs of New York might have recognized the faces of men whose pictures were in the rogues' gallery and who were members of those various aristocratic organizations of the underworld.

Kennedy glanced about at the motley crowd. "This is a place where you need only to be introduced properly," he whispered to me, "to have any kind of crime committed for you."

As we stood there, observing, without appearing to do so, through an open window on the side street I could tell from the sounds that there was a garage in the rear of the hotel.

We were startled to hear a sudden uproar from the street.

Garwood, impatient at our delay, had walked down past the garage to reconnoiter. A car was being backed out hurriedly, and as it turned and swung around the corner, his trained eye had recognized it.

Instantly he had reasoned that it was an attempt to make a getaway, and had raised an alarm.

Those nearest the door piled out, keen for any excitement. We, too, dashed out on the street. There we saw passing an automobile, swaying and lurching at the terrific speed with which its driver, urged it up the avenue. As he flashed by he looked like an Italian to me, perhaps a gunman.

Garwood had impressed a passing trolley car into service and was pursuing the automobile in it, as it swayed on its tracks as crazily as the motor did on the roadway, running with all the power the motorman could apply.

A mounted policeman galloped past us, blazing away at the tires. The avenue was stirred, as seldom even in its strenuous life, with reports of shots, honking of horns, the clang of trolley bells and the shouts of men.

The pursuers were losing when there came a rattle and roar from the rear wheels which told that the tires were punctured and the heavy car was riding on its rims. A huge brewery wagon crossing a side street paused to see the fun, effectually blocking the road.

The car jolted to a stop. The chauffeur leaped out and a moment later dived down into a cellar. In that congested district, pursuit was useless.

"Only an accomplice," commented Kennedy. "Perhaps we can get him some other way if we can catch the man—or woman—higher up."

Down the street now we could see Garwood surrounded by a curious crowd but in possession of the car. I looked about for Duncan and Reginald. They had apparently been swallowed up in the crowds of idlers which seemed to be pouring out of nowhere, collecting to gape at the excitement, after the manner of a New York crowd.

As I ran my eye over them, I caught sight of Reginald near the corner where we had left him in an incipient fight with someone who had a fancied grievance. A moment later we had rescued him.

"Where's Duncan?" he panted. "Did anything happen to him? Garwood told us to stay here—but we got separated."

Policemen had appeared on the heels of the crowd and now, except for a knot following Garwood, things seemed to be calming down.

The excitement over, and the people thinning out, Kennedy still could not find any trace of Duncan. Finally he glanced in again through the swinging doors. There was Duncan, evidently quite upset by what had occurred, fortifying himself at the bar.

Suddenly from above came a heavy thud, as if someone had fallen on the floor above us, followed by a suppressed shuffling of feet and a cry of help.

Kennedy sprang toward a side door which led out into the hall to the hotel room above. It was locked. Before any of the others he ran out on the street and into the hall that way, taking the stairs two at a time, past a little cubby-hole of an "office" and down the upper hall to a door from which came the cry.

It was a peculiar room into which we burst, half bedroom, half workshop, or rather laboratory, for on a deal table by a window stood a rack of test-tubes, several beakers, and other paraphernalia.

A chambermaid was shrieking over a woman who was lying lethargic on the floor.

I looked more closely.

It was Dora Sears.

For the moment I could not imagine what had happened. Had the events of the past few days worked on her mind and driven her into temporary insanity? Or had the blackmailing gang of automobile thieves, failing in extorting money by their original plan, seized her?

Kennedy bent over and tried to lift her up. As he did so, the gold bracelet, unclasped, clattered to the floor.

He picked it up and for a moment looked at it. It was hollow, but in that part of it where it unclasped could be seen a minute hypodermic needle and traces of a liquid.

"A poison bracelet," he muttered to himself, "one in which enough of a virulent poison could be hidden so that in an emergency death could cheat the law."

"But this Dr. Hopf," exclaimed Reginald, who stood behind us looking from the insensible girl to the bracelet and slowly comprehending what it all meant, "she alone knows where and who he is!"

We looked at Kennedy. What was to be done? Was the criminal higher up to escape because one of his tools had been cornered and had taken the easiest way to get out?

Kennedy had taken down the receiver of the wall telephone in the room. A moment later he was calling insistently for his laboratory. One of the students in another part of the building answered. Quickly he described the apparatus for vividiffusion and how to handle it without rupturing any of the delicate tubes.

"The large one," he ordered, "with one hundred and ninety-two tubes.
And hurry."

Before the student appeared, came an ambulance which some one in the excitement had summoned. Kennedy quickly commandeered both the young doctor and what surgical material he had with him.

Briefly he explained what he proposed to do and before the student arrived with the apparatus, they had placed the nurse in such a position that they were ready for the operation.

The next room which was unoccupied had been thrown open to us and there I waited with Reginald and Duncan, endeavoring to explain to them the mysteries of the new process of washing the blood.

The minutes lengthened into hours, as the blood of the poisoned girl coursed through its artificial channel, literally being washed of the toxin from the poisoned bracelet.

Would it succeed? It had saved the life of Buster. But would it bring back the unfortunate before us, long enough even for her to yield her secret and enable us to catch the real criminal. What if she died?

As Kennedy worked, the young men with me became more and more fascinated, watching him. The vividiffusion apparatus was now in full operation.

In the intervals when he left the apparatus in charge of the young ambulance surgeon Kennedy was looking over the room. In a trunk which was open he found several bundles of papers. As he ran his eye over them quickly, he selected some and stuffed them into his pocket, then went back to watch the working of the apparatus.

Reginald, who had been growing more and more nervous, at last asked if he might call up Betty to find out how his mother was.

He came back from the telephone, his face wrinkled.

"Poor mother," he remarked anxiously, "do you think she will pull through, Professor? Betty says that Dr. Wilson has given her no idea yet about the nature of the trouble."

Kennedy thought a moment. "Of course," he said, "your mother has had no such relative amount of the poison as Buster has had. I think that undoubtedly she will recover by purely natural means. I hope so. But if not, here is the apparatus," and he patted the vividiffusion tubes in their glass case, "that will save her, too."

As well as I could I explained to Reginald the nature of the toxin that Kennedy had discovered. Duncan listened, putting in a question now and then. But it was evident that his thoughts were on something else, and now and then Reginald, breaking into his old humor, rallied him about thinking of Betty.

A low exclamation from both Kennedy and the surgeon attracted us.

Dora Sears had moved.

The operation of the apparatus was stopped, the artery and vein had been joined up, and she was slowly coming out from under the effects of the anesthetic.

As we gathered about her, at a little distance, we heard her cry in her delirium, "I—I would have—done—anything—for him."

We strained our ears. Was she talking of the blackmailer, Dr. Hopf?

"Who?" asked Craig, bending over close to her ear.

"I—I would—have done anything," she repeated as if someone had contradicted her. She went on, dreamily, ramblingly, "He—is—is—my brother. I—"

She stopped through weakness.

"Where is Dr. Hopf?" asked Kennedy, trying to recall her fleeting attention.

"Dr. Hopf? Dr. Hopf?" she repeated, then smiling to herself as people will when they are leaving the borderline of anesthesia, she repeated the name, "Hopf?"

"Yes," persisted Kennedy.

"There is no Dr. Hopf," she added. "Tell me—did—did they—"

"No Dr. Hopf?" Kennedy insisted.

She had lapsed again into half insensibility.

He rose and faced us, speaking rapidly.

"New York seems to have a mysterious and uncanny attraction for odds and ends of humanity, among them the great army of adventuresses. In fact there often seems to be something decidedly adventurous about the nursing profession. This is a girl of unusual education in medicine. Evidently she has traveled—her letters show it. Many of them show that she has been in Italy. Perhaps it was there that she heard of the drug that has been used in this case. It was she who injected the germ-free toxin, first into the dog, then into Mrs. Blake, she who wrote the blackmail letter which was to have explained the death."

He paused. Evidently she had heard dimly, was straining every effort to hear. In her effort she caught sight of our faces.

Suddenly, as if she had seen an apparition, she raised herself with almost superhuman strength.

"Duncan!" she cried. "Duncan! Why—didn't you—get away—while there was time—after you warned me?"

Kennedy had wheeled about and was facing us. He was holding in his hand some of the letters he had taken from the trunk. Among others was a folded piece of parchment that looked like a diploma. He unfolded it and we bent over to read.

It was a diploma from the Central Western College of Nursing. As I read the name written in, it was with a shock. It was not Dora Sears, but Dora Baldwin.

"A very clever plot," he ground out, taking a step nearer us. "With the aid of your sister and a disreputable gang of chauffeurs you planned to hasten the death of Mrs. Blake, to hasten the inheritance of the Blake fortune by your future wife. I think your creditors will have less chance of collecting now than ever, Duncan Baldwin."