When we reached the entrance to our quarters on Montgomery Street the rain had once more begun to fall, gently now, but the gusts of damp wind from the south promised more and worse to follow.

“Hello!” cried the first man, starting back. “What's this?”

The line stopped, and I moved forward.

“What is it?” I asked.

“A message for you, Mr. Wilton,” said a voice suddenly from the recess of the doorway.

“Give it to me,” I said.

A slip of paper was thrust into my hand, and I passed up the stairs.

“I'll wait for you,” said the messenger, and at the first gas-jet that burned at the head of the stairs I stopped to read the address.

It was in the hand of the Unknown, and my fatigue and indifference were gone in a moment. I trembled as I tore open the envelope, and read:

“Follow the bearer of this note at 12:30. Come alone and armed. It is important.”

There was no signature.

If this meant anything it meant that I was to meet the Unknown, and perhaps to search the heart of the mystery. I had been heavy with fatigue and drowsy with want of sleep, but at this thought the energies of life were once more fresh within me.

With my new-found knowledge it might be more important than even the Unknown was aware, that we should meet. To me, the map, the absence of Darby Meeker and his men, the mysterious hints of murder and death that had come from the lips of Mother Borton, were but vaguely suggestive. But to the Unknown, with her full knowledge of the objects sought by the enemy and the motives that animated their ceaseless pursuit, the darkness might be luminous, the obscurity clear.

The men had waited a minute for me as I read the note.

“Go to your rooms and get some rest,” I said. “I am called away. Trent will be in charge, and I will send word to him if I need any of you.”

They looked at me in blank protest.

“You're not going alone, sir?” cried Owens in a tone of alarm.

“Oh, no. But I shall not need a guard.” I hoped heartily that I did not.

The men shook their heads doubtfully, and I continued:

“Corson will be down from the Central Station in fifteen or twenty minutes. Just tell him that I've been sent for, and to come to-morrow if he can make it in his way.”

And bidding them good night I ran hastily down the stairs before any of the men could frame his protest into words.

“Are you ready, sir?” asked the messenger.

“It is close on half-past twelve,” I answered. “Where is she?”

“It's not far,” said my guide evasively.

I understood the danger of speech, and did not press for an answer.

We plunged down Montgomery Street in the teeth of the wind that dashed the spray in our faces at one moment, lulled an instant the better to deceive the unwary, and then leaped at us from behind corners with the impetuous rush of some great animal that turned to vapor as it reached us. The street was dark except for the newspaper offices, which glowed bright with lights on both sides of the way, busy with the only signs of life that the storm and the midnight hour had left.

With the lighted buildings behind us we turned down California Street. Half-way down the block, in front of the Merchants' Exchange, stood a hack. At the sight my heart beat fast and my breath came quick. Here, perhaps, was the person about whom centered so many of my hopes and fears, in whose service I had faced death, and whose words might serve to make plain the secret springs of the mystery.

As we neared the hack my guide gave a short, suppressed whistle, and passing before me, flung open the door to the vehicle and motioned me to enter. I glanced about with some lack of confidence oppressing my spirits. But I had gone too far to retreat, and stepped into the hack. Instead of following, the guide closed the door gently; I heard him mount the seat by the driver, and in a moment we were in motion.

Was I alone? I had expected to find the Unknown, but the dark interior gave no sign of a companion. Then the magnetic suggestion of the presence of another came to my spirit, and a faint perfume put all my senses on the alert. It was the scent that had come to me with the letters of the Unknown. A slight movement made me certain that some one sat in the farther corner of the carriage.

Was it the Unknown or some agent? And if it proved to be the Unknown, was she the lady I had met in cold business greeting in the courtyard of the Palace Hotel? I waited impatiently for the first street-lamp to throw a gleam of light into the carriage. But when it came I was little the wiser. I could see faintly the outlines of a figure shrouded in black that leaned in the corner, motionless save for the swaying and pitching of the hack as it rolled swiftly down the street.

The situation became a little embarrassing. Was it my place to speak first? I wondered. At last I could endure the silence no longer.

“Quite an unpleasant evening,” I remarked politely.

There was a rustle of movement, the sound of a short gasp, and a soft, mournful voice broke on my ear.

“Mr. Dudley—can you forgive me?”

The astonishment I felt to hear my own name once more—the name that seemed now to belong to a former state of existence—was swallowed up as the magnetic tones carried their revelation to my mind.

I was stricken dumb for a moment at the discovery they had brought. Then I gasped:

“Mrs. Knapp!”

“Yes, Mrs. Knapp,” she said with a mournful laugh. “Did you never suspect?”

I was lost in wonder and confusion, and even yet could not understand.

“What brings you out in this storm?” I asked, completely mystified. “I thought I was to meet another person.”

“Indeed?” said Mrs. Knapp with a spark of animation. “Well, I am the other person.”

I was paralyzed in mind and nerve for a moment with the astonishment of the disclosure. Even yet I could not believe.

“You!” I exclaimed at last. “Are you the protector of the boy? The employer—” Then I stopped, the tangle in my mind beginning to straighten out.

“I am she,” said Mrs. Knapp gently.

“Then,” I cried, “who is he? what is he? what is the whole dreadful affair about? and what—”

Mrs. Knapp interrupted me.

“First tell me what has become of Henry Wilton?” she said with sorrow in her voice.

The dreadful scene in the alley flashed before my mind.

“He is dead.”

“Dead! And how?”

“Murdered.”

“I feared so—I was certain, or he would have let me know. You have much to tell me. But first, did he leave no papers in your hands?”

I brought out the slip that bore the blind diagram and the blinder description that accompanied it. Nothing could be made of it in the darkness, so I described it as well as I could.

“We are on the right track,” said Mrs. Knapp. “Oh, why didn't I have that yesterday? But here—we are at the wharf.”

The hack had stopped, and a hand was fumbling at the door.

The darkness, the dash of water, the wind whistling about the crazy wooden buildings and through the rigging of ships, made the water-front vocal with the shouting of the storm demons as we alighted.

My guide was before us, and we followed him down the pier, struggling against the gusts.

“Do we cross the bay?” I asked, as Mrs. Knapp clung to my arm. “It's not safe for you in a small boat.”

“There's a tug waiting for us,” Mrs. Knapp explained.

A moment later we saw its lights, and the fire of its engine-room shot a cheerful glow into the storm. The little vessel swung uneasily at its berth as we made our way aboard, and with shouts of men and clang of bells it was soon tossing on the dark waters of the bay. Out from the shelter of the wharves the wind buffeted us wildly, and the black waves were threshed into phosphorescent foam against the sides of the tug, while their crests, self-luminous, stretched away in changing lines of faint, ghostly fire.

The cabin of the tug was fitted with a shelf table, and over it swung a lamp of brass that gave a dim light to the little room. Mrs. Knapp seated herself here, as the boat pitched and tossed and trembled at the strokes of the waves and quivered to the throbbing of the screw, spread out the paper I had given her, and studied the diagram and the jumble of letters with anxious attention.

“It is the same,” she said at last; “in part, at least.”

“The same as what?” I asked.

“As the one I got word of to-night, you know,” she replied.

“No—I didn't know.”

“Of course not,” said Mrs. Knapp. “But you might have guessed that I got my summons after you left, this evening. I should have spoken to you then if I had known. I was near coming to an explanation, as it was.”

“There are a good many things I haven't guessed,” I confessed.

“But,” she continued, returning to the map, “this gives a different place. I was to go to the cross-road here,”—indicating the mark at the last branch.

“I'm glad to hear that,” said I, taking out the diagram I had found in the citadel of the enemy. “This seems to point to a different place, too, and I really hope that the gentleman who drew this map is a good way off from the truth.”

“Where did you get this?” exclaimed Mrs. Knapp.

I described the circumstances in as few words as I could command.

“They are ahead of us,” she said in alarm.

“They have started first, I suppose,” was my suggestion.

“And they have the right road.”

“Then our only hope is that they may not know the right place.”

“God grant it,” said Mrs. Knapp.

She was silent for a few minutes, and I saw that her eyes were filled with tears.

I was moved by her signs of feeling. I thought they were for the boy and was about to ask what would happen to him in case he was found by the enemy, when she said:

“Now tell me about Henry Wilton—how he died and when.”

Again the vision of my first dreadful night in San Francisco rose before me, the cries for help from my murdered friend rang in my ears, and the scene in the alley and the figure in the morgue burned before my eyes.

I told the tale as it had happened, and as I told it I read in the face before me the varying emotions of alarm, horror and grief that were stirred by its incidents.

But one thing I could not tell her. The wolf-face I had seen in the lantern flash in the alley I could not name nor describe to the wife of Doddridge Knapp. Yet at the thought the dark mystery grew darker, yet, and I began to doubt what my eyes had seen, and my ears had heard.

Mrs. Knapp bowed her head in deep, gloomy thought.

“I feared it, yet he would not listen to my warnings,” she murmured. “He would work his own way.” Then she looked me suddenly straight in the face.

“And why did you take his place, his name? Why did you try to do his work when you had seen the dreadful end to which it had brought him?”

I confessed that it was half through the insistence of Detective Coogan that I was Henry Wilton, half through the course of events that seemed to make it the easiest road to reach the vengeance that I had vowed to bring the murderer of my friend.

“You are bent on avenging him?” asked Mrs. Knapp thoughtfully.

“I have promised it.”

“You shall have the chance. Strange thought!” she said gloomily, “that the dead hand of Henry Wilton may reach out from beyond the grave and strike at his slayer when he least expects it.”

I was more than ever mystified at these words. I had not expected her to take so philosophically to the idea of hanging Doddridge Knapp, and I thought it best to hold my tongue.

“I have marveled at you,” said Mrs. Knapp after a pause. “I marvel at you yet. You have carried off your part well.”

“Not well enough, it seems, to deceive you,” I said, a little bitterly.

“You should not have expected to deceive me,” said Mrs. Knapp. “But you can imagine the shock I had when I saw that it was not Henry Wilton who had come among us that first night when I called you from Mr. Knapp's room.”

“You certainly succeeded in concealing any surprise you may have felt,” I said. “You are a better actor than I.”

Mrs. Knapp smiled.

“It was more than surprise—it was consternation,” she said. “I had been anxious at receiving no word from Henry. I suppose you got my notes. And when I saw you I was torn with doubts, wondering whether anything had happened to Henry, whether he had sent you in his stead as a practical joke, whether you knew much or little or nothing of our affairs—in short, I was overwhelmed.”

“I didn't suppose I was quite so poor an impostor,” I said apologetically, with a qualm at the word. “Though I did get some hint of it,” I added, with a painful recollection of the candid statement of opinion I had received from the daughter of the house.

“Oh, you did very well,” said Mrs. Knapp kindly, “but no one could have been successful in that house. Luella was quite outraged over it, but I managed to quiet her.”

“I hope Miss Knapp has not retained the unfavorable impressions of—er—” I stammered in much confusion.

Mrs. Knapp gave me a keen glance.

“You know she has not,” she said.

I felt the subconscious impression somehow that after all Mrs. Knapp would have been better pleased if Luella had kept nearer to her first impressions of me.

“Well,” continued Mrs. Knapp, “when I saw you and guessed that something had happened to Henry Wilton, and found that you knew little of what was going on, I changed the plan of campaign. I did not know that you were one to be trusted, but I saw that you could be used to keep the others on a false scent, for you deceived everybody but us.”

“There was one other,” I said.

“Mother Borton?” inquired Mrs. Knapp. “Yes, I learned that she knew you. But to every one else in the city you were Henry Wilton. I feared, though, you would make some mistake that would betray you and spoil my plans. But you have succeeded marvelously.”

Mrs. Knapp paused a moment and then continued slowly. “It was cruel of me. I knew that it was sending you to face death. But I was alarmed, angry at the imposition, and felt that you had brought it on yourself. Can you forgive me?”

“I have nothing to forgive,” I said.

“I would have spoken when I found you for what you are,” said Mrs. Knapp, “but I thought until the Livermore trip that you could serve me best as you were doing.”

“It was blind work,” I said.

“It was blind enough for you, not for me. I was deceived in one thing, however; I thought that you had no papers—nothing from Henry that could help or hurt. The first night you came to us I had Henry's room thoroughly searched.”

“Oh, I was indebted to you for that attention,” I exclaimed. “I gave our friends of the other house the credit.”

Mrs. Knapp smiled again.

“I thought it necessary. It was the chance that you did not sleep there that night that kept this paper out of my hands weeks ago.”

“I have always kept it with me,” I said.

“I did not need it till Sunday,” continued Mrs. Knapp. “I have been worried much at the situation of the boy, but I did not dare go near him. Henry and I decided that his hiding-place was not safe. We had talked of moving him a few days before you came. When I found that Henry had disappeared I was anxious to make the change, but I could not venture to attempt it until the others were out of town, for I knew I was watched. Then I was assured from Mother Borton that they did not know where the boy was hidden, and I let the matter rest. But a few days ago—on Saturday—she sent me word that she thought they had found the place. Then it came to me to send you to Livermore with the other boy—oh, I hope no harm came to the little fellow,” she exclaimed anxiously.

“He's safe at my rooms in charge of Wainwright,” I said. “He got back on the morning train, and can be had for the asking.”

“Oh, I'm so glad,” said Mrs. Knapp. “I was afraid something would happen to him, but I had to take desperate chances. Well, you see my plan succeeded. They all followed you. But when I went to the hiding-place the boy was gone. Henry had moved him weeks ago, and had died before he could tell me. Then I thought you might know more than you had told me—that Henry Wilton might have got you to help him when he made the change, and I wrote to you.”

“And the key,” I said, remembering the expression of the note, “Did you mean this diagram?”

“No,” said Mrs. Knapp. “I meant the key to our cipher code. I was looking over Henry's letters for some hint of a hiding-place and could not find the key to the cipher. I thought you might have been given one. I found mine this afternoon, though, and there was no need of it, so it didn't matter after all.”

The pitching and tossing of the boat had ceased for some minutes, and at this point the captain of the tug opened the cabin.

“Excuse me,” he said apologetically, uncertain whether to address Mrs. Knapp or me, and including us both in the question, “but where did you want to land?”

“At Broadway,” said Mrs. Knapp.

“Then you're there,” said the captain.

And, a minute later, with clang of bells and groan of engine we were at the wharf and were helped ashore.

On this side of the bay the wind had fallen, and there were signs of a break in the clouds. The darkness of the hour was dimly broken by the rays from the lines of street-lamps that stretched at intervals on both sides of Broadway, making the gloom of the place and hour even more oppressive.

“Tell the captain to wait here for us with fires up,” said Mrs. Knapp. “The carriage should be somewhere around here,” she continued, peering anxiously about as we reached the foot of the wharf.

The low buildings by the railroad track were but piles of blackness, and about them I could see nothing.

“This way,” said a familiar voice, and a man stepped from the shadow.

“Dicky Nahl!” I exclaimed.

“Mr. Wilton!” mimicked Dicky. “But it's just as well not to speak so loud. Here you are. I put the hack's lights out just to escape unpleasant remark. We had better be moving, for it's a stiffish drive of six or seven miles. If you'll get in, I'll keep the seat with the driver and tell him the way to go.”

Mrs. Knapp entered the carriage, and called to me to follow her.

I remembered Mother Borton's warnings and my doubts of Dicky Nahl.

“You're certain you know where you are going?” I asked him in an undertone.

“No, I'm not,” said Dicky frankly. “I've found a man who says he knows. We are to meet him. We'll get there between three and four o'clock. He won't say another word to anybody but her or you. I guess he knows what he is about.”

“Well, keep your eyes open. Meeker's gang is ahead of us. Is the driver reliable?”

“Right as a judge,” said Dicky cheerfully, “Now, if you'll get in with madam we won't be wasting time here.”

I stepped into the carriage. Dicky Nahl closed the door softly and climbed on the seat by the driver, and in a moment we were rolling up Broadway in the gloomy stillness of the early morning hour.