Duvall, on his arrival with Mrs. Morton at her apartment, lost no time in finding out from the clerk just what had happened. The story, pieced together, confirmed his worst suspicions.

The woman, after escaping from the house at 162 West 57th Street, had gone at once to Ruth's hotel, followed by Grace. Here she had interviewed Mrs. Morton, represented herself as Grace Duvall, and induced Mrs. Morton to leave the hotel by giving her a fictitious message purporting to be from himself.

Returning, later, to the hotel, she had gone to Ruth Morton's room and attacked her. The nature of that attack, the effect upon the girl, were as yet uncertain. Ruth Morton was still unconscious.

Meanwhile, as he learned from the clerk, Grace had received a telephone message and hurriedly left the hotel. The clerk did not know from whom the message had come.

Duvall went to Ruth Morton's bedroom, and called the doctor aside.

"What is the exact nature of Miss Morton's injuries?" he asked.

"She has no injuries, at least in the sense I think you mean. She is suffering solely from the effects of shock."

"What sort of shock?"

"I do not know, of course. Fright, of some sort, terrible fright, I should say. I am informed that some woman, some enemy of hers, came to this room, and was alone with her."

"There is no evidence of any violence?"

"None whatever. But the effects of shock are often worse than those of actual physical violence. They have frequently been known to cause death."

"You do not, I hope, anticipate anything of the sort in this case."

"I cannot say." The doctor shook his head. "She must have been very weak. Her system is responding very slowly."

Duvall glanced over to where Mrs. Morton hung in agonized silence over her daughter's bed, then went out into the sitting room. It seemed to him well nigh incredible that the woman responsible for all this had been able to move about, to elude pursuit, to carry out her threats, apparently without the least hesitation or fear of capture. His professional pride had received severe shock.

Two means of finding the woman, he felt, were still open to him. One was to trace her through Miss Ford. He did not doubt that, after what he had said to the latter, she would make an immediate attempt to warn her confederate of the danger that threatened her. Of course, the Ford girl might communicate with her companion by telephone, in which event the tracing would be difficult, if not impossible.

The other hope of tracing the woman lay in Grace. Why had she left the hotel so suddenly? He did not of course know the source of the telephone message, and could only surmise that Grace had in some way been able to pick up the woman's trail.

Leaving Mrs. Morton with a few words of encouragement, he made his way to his hotel. There was no news there of Grace, however, and he realized that it was now too late to accomplish anything by returning to the house on 57th Street. Marcia Ford would either have long since retired, or else would have left the house to communicate with the woman who had been with her earlier in the evening. Considerably upset by the events of the past three hours, Duvall retired to his room, and sat down to think the whole matter over.

Proceeding on the assumption that the woman in question, and Miss Ford were acting together, all the events at the studio, the fake telegram, the missing photograph, became intelligible. But the delivery of the letters in Ruth Morton's apartment, the strange attack upon him while searching the Ford girl's room, were by no means so clear. Once more his thoughts reverted to the attic room, the roof of the adjoining house, the problem of effecting an entrance to the Morton apartment through either of the two windows.

And then, as he revolved the problem in his mind, a sudden light came to him. He sprang from his chair with an exclamation of satisfaction. A solution of the whole matter flashed through his brain, a solution at once so simple, and so ingenious, that he wondered he had not thought of it before.

He glanced at his watch. It was midnight. Too late, perhaps, to test the accuracy of his deductions. Nor did he feel at all easy in his mind regarding Grace. Something must have happened to her, he feared, to keep her out so late, with no word to him concerning her movements. He went to the 'phone, and calling up the office, inquired whether anything had been heard of Mrs. Duvall.

"No," the night clerk informed him. Mrs. Duvall had not been heard from, nor had she sent any message. But a note had just been left for her. He would send it up.

Duvall awaited the arrival of the note with the utmost impatience. A message for Grace. From whom? What could it mean? A few moments later one of the bellboys thrust into his hand a letter, written on the note paper of the hotel.

He regarded the scrawling and ill-written superscription with apprehension, then tore open the envelope and proceeded to read the contents of the note.

"Dear Madam," it said. "I waited till nearly midnight. When you did not come, I thought you must have gone out some other way, so came back to the hotel. I hope I did right. Respectfully yours, Martin Leary." Duvall stared at the words before him with a look of alarm. Who was Martin Leary? And where had he waited for Grace until nearly midnight? And, above all, why had she not returned? Had some accident, some danger befallen her? The circumstances made it seem highly probable.

There was but one thing to do—to question the night clerk, and find out, if possible, who Leary was. He rushed to the elevator and made his way to the lobby with all speed.

"Who left this note for Mrs. Duvall?" he asked of the clerk.

"Why,"—the man paused for a moment—"one of the cabmen, I believe."

"Is his name Leary—Martin Leary?"

"Yes. It was Leary, come to think of it. Nothing wrong, I hope, Mr. Duvall."

"I'll know later. Where is Leary now?"

"Couldn't say, sir. You might ask the cab starter?"

Almost before the clerk had finished speaking, Duvall had darted across the lobby and made his way to the taxicab office at the door.

"Taxi, sir?" the man asked. "Do you know a chauffeur named Martin Leary?" exclaimed Duvall.

"Yes, sir. One of our regular men, sir."

"Where is he?"

The starter glanced along the row of taxicabs.

"He's turned in for the night, sir. Left for the garage some time ago. He's been on duty since early this morning."

"Where is the garage?"

"On Lexington Avenue, sir, near 30th Street."

"Does Leary sleep there?"

"No, sir. I don't think so, sir. They would know at the garage, I guess."

"Very well. Get me a cab. I want to be taken there at once."

The starter called to one of the drivers, and a few moments later Duvall was being driven at a rapid rate toward the garage.

His inquiries, on his arrival there, developed the fact that Leary had left for his home, on Second Avenue, some little time before. Duvall secured the address, and once more set out.

He felt greatly alarmed at Grace's failure to put in an appearance. Something must have happened to her. Clearly the case was going very much against him—the woman's second escape—the attack on Ruth Morton—now the disappearance of Grace. He felt that the time had come for action of a quick and drastic nature.

Leary lived with his wife and two children on the third floor of a Second Avenue tenement. Hastily climbing the two flights of dark steps, Duvall rapped on the door. He was overjoyed when it was opened by a man whom he judged to be the chauffeur himself.

"Are you Martin Leary?" he asked.

"Yes, sir." The man wiped his mouth with the back of his hand, choking down a bit of cold supper he had been eating, before turning in.

"I am Richard Duvall. You drove my wife uptown, somewhere, did you not?"

"Yes, sir. To Columbus Avenue and Ninety-sixth Street, sir. Won't you come in?"

"No. There isn't time. I want you to put on your coat and come along with me. Mrs. Duvall has not returned, and I am afraid something has happened to her."

The man turned and called to someone inside the flat.

"Gimme my hat and coat, Kitty," he said, then turned again to Duvall. "I suppose I should have waited, sir, but after two hours went by, I made up my mind that Mrs. Duvall didn't need me any longer."

"What is the building at Columbus Avenue and 96th Street?" Duvall asked, as the man, pulling on the coat his wife handed him, strode down the hall.

"An apartment building, sir."

"And why did Mrs. Duvall go there?"

"Well, sir, we was following a woman, sir. She went to a hotel on Seventy-second Street, and Mrs. Duvall told me to watch for her. I did, and tracked her to the place at 96th Street. Then I telephoned to Mrs. Duvall to come, and she did."

"What time was that?"

"About half-past nine, sir."

"All right. Go on."

"Mrs. Duvall came, sir, in another taxi. I pointed out the place where the woman went in, and Mrs. Duvall went in after her. She didn't say I was to wait, but I guess she expected me to, because she had sent the other cab away. I waited over two hours, and then, when she didn't come out, I supposed she had returned to her hotel, so I came back, too. She wasn't there, though. That's why I left the note."

"How did you think Mrs. Duvall could have gotten back to her hotel, if you were watching the door of the apartment house all the time?"

"I wasn't watching it all the time, sir. I went into the drug store once, sir, and got a cigar. And then, later on, I went to a saloon a piece down the Avenue and got a glass of beer. Mrs. Duvall didn't say I was to watch the place, sir. I thought when she got through what she had to do, she would come back to the cab. But she didn't. Do you think I ought to have waited, sir?" The man seemed greatly distressed.

"No use talking about that now," Duvall remarked, shortly. "I want to drive there at once. Get on the box, with the chauffeur, and point out the place to him."

"Yes, sir." A moment later they had started on their way uptown.

Knowing as he did Grace's impetuous nature, Duvall could only conclude that her pursuit of the woman had led her into some trap. What danger she might at this moment be facing, he could only surmise. The apartment building, when they finally reached it, presented a grim and forbidding appearance. Not a light broke the darkness of any of its windows. The drug store on the opposite corner, too, was closed for the night. The whole locality was dark and silent.

"There's the place, sir," Leary exclaimed, as they drew up to the corner.

"Tell the driver to stop a few doors up the block—not right in front of the building."

Leary nodded. Presently the cab stopped, and he and Duvall got out.

The detective's first move was to ascertain whether or not the building had any rear exit, by which Grace might have left, without being seen by Leary. He walked down the avenue to its rear wall, only to find that it abutted against the wall of the next building. There was no rear entrance.

If, then, Grace had not left the place during the past hour, she must still be in one of the ten flats that formed the five floors of the building. But which one? That, apparently, was the problem he had to solve.

It would be useless, he felt, to inquire at the doors of the various apartments at this hour of the morning. Admission, at least on the part of those he sought, would certainly be refused. Yet he felt that there was no time to be lost.

Stationing Leary before the front door, with instructions to keep a careful watch, Duvall went into the vestibule, and by means of his pocket light, inspected the names of the occupants of the building, as Grace had done a short time before. The hallway inside was dark, with the exception of a dim light at the foot of the stairs. Apparently the place boasted no elevator or hall-boy service.

The ten names on the boxes in the vestibule meant nothing to him. How was it possible to determine which one was that of the woman he sought? Weinberg—Scully—Martin—Stone—he ran down the list, trying to find some distinguishing mark, some clue, that would guide him.

Suddenly he paused, allowing the light from his torch to rest upon the card bearing the name of one of the tenants on the fourth floor.

This card had attracted his attention, because it was different from any of the others in the two racks. They were either engraved or printed visiting cards, stuck inside the brass frames provided for them, or the names were written or printed by hand upon blank cards. But this card, bearing simply the inscription E. W. Norman, was neither engraved nor printed, nor written by hand. On the contrary, it was typewritten.

This in itself at once attracted Duvall's attention, owing to the fact that the various letters received by Ruth Morton had also all been typewritten. If the name, Norman, was an assumed one, as Duvall concluded it to be, what more natural than that it should be typewritten on a blank card, especially when a regular printed or engraved card was not available; when to have it written in long hand would have been a disclosure of identity, and when, above all, the woman in question possessed, and knew how to operate, a typewriter.

There was more than this, however, about the name on the card, to convince Duvall that E. W. Norman was the woman he sought. He recalled with distinctness the two salient features of the typewriting in all the letters sent to Miss Morton, the misplaced "a," and the broken lower right-hand corner of the capital "W." He looked closely at the two letters in the name before him. The "a" was misplaced, the "W" minus its lower right-hand corner. The evidence seemed to be complete.

The next thing to be considered was, how could he first obtain entrance to the apartment building, and, subsequently, to the flat of the woman posing as E. W. Norman? Were he to ring the latter's bell, he felt quite sure she would not respond by unfastening the front door, but she would on the contrary be warned, and even if unable to escape, might destroy the evidence he hoped to find in her possession.

On the other hand, to ring the bell of one of the other apartments might result in the unlatching of the front door, but might involve explanations, difficult, in the circumstances, to make. There was no help for it, however. Duvall pressed the bell belonging to the family named Scully.

It was a long time before there was any response. Duvall had almost begun to despair of getting one, when he heard the clicking of the electric latch, and found that he could turn the knob and enter the hallway.

He had barely done so, when at big, burly-looking man, who might have been a bartender, or a head waiter, appeared in the door of one of the ground floor apartments, clad only in his night clothes.

"Well—whatcha want?" he growled.

Duvall stepped up to him quickly, and spoke in a pleasant voice.

"I'm mighty sorry," he said. "I rang your bell by mistake. Pardon me."

The man glared at him, suspicion blazing from his eyes.

"That's an old one," he retorted. "How do I know you ain't a burglar?"

"Do I look like one?" Duvall asked.

The man ignored this question.

"Rang my bell by mistake, did you? Who do you want to see?"

"I have some business with a lady on the fourth floor." He went closer to the man, and lowered his voice. "I'm a detective, my friend," he whispered confidentially. "I'm here on a very important case."

The big man's eyes widened.

"Th' hell you are!" he exclaimed. "Central office?"

"No. Private."

"H—m." The man nodded slowly. "All right. But I guess I'll keep my eye on you, just the same." He leaned against the door jamb and watched Duvall as he ascended the stairs.

The detective reached the fourth floor at top speed. He was panting, when he arrived opposite the door of the apartment he sought. Once there, he paused for a moment, listening intently. Not a sound came from the interior of the flat.

The problem of obtaining access to the place now confronted him. The door was of oak of stout construction. He doubted his ability to break it in, nor did he wish to attempt to do so, if it could be avoided. Breaking into private apartments, without a warrant, was a serious matter. There was a chance that this might not be the right place, after all. He hesitated. Yet Grace might be within, in danger, perhaps, of her life. It was imperative that he should find out the truth at once.

Stepping up to the door, he knocked sharply upon it, then waited for a reply. He scarcely expected one, but felt that he should at least give the persons within a chance.

A long silence ensued. Duvall was about to rap again, when, to his amazement, the door slowly and noiselessly swung inward, as though impelled by some unseen hand.

The room beyond was shrouded in darkness. Duvall could see no one. Whoever had opened the door must now be concealed behind it. No one either greeted or challenged him. The door swung three-quarters open, and stood still. Not a sound was to be heard. The room was as silent as a tomb.

Duvall stood on the threshold for a few seconds, listening intently. He was greatly astonished by what had occurred. Why had the door been so silently opened? Was someone waiting within, ready to attack him the moment he made a step forward?

Whether this was the case or not, nothing, he reflected, was to be gained by remaining where he was. Drawing an automatic pistol from his pocket, he held it in readiness in his right hand, then, raising his left arm, he flung his entire weight against the partly opened door.

The door yielded to his attack. Then there came a dull thud, as though some heavy body had fallen to the floor, and immediately after the hallway resounded with a series of unearthly screams. Duvall still moved forward. Then, to his utter surprise, there appeared in the darkness a grotesque figure, which immediately hurled itself upon him and began to clutch frantically at his throat.