"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 gla.s.s 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."