I heard the movement of heavy metal locks and latches; the door swung back and I found myself standing before a middle-aged woman dressed in the black-and-white garb of well-trained servants.

This woman had a face that one may find sometimes among veteran nuns—a strong and kindly face, patient and self-subjugated—the face of the convent. But, of course, old family serving-women may have this same expression, for they too are nuns in a sense; in household rites they renounce the world, and if the spirit does not sour, little by little, they take wordless vows and obliterate themselves in service. This woman who stood before me, with skirts and apron blown about her substantial figure by the chill wind that poured into the vestibule, seemed at first to be one of them. It was only when I perceived that her eyes were filled with some guilty fear, and that her hands were half raised as if to ward off some impending danger, that I began to suspect that hers was one of those masks which hypocrisy and deceit grow upon the countenance of evil souls.

“I wish to see Mr. Estabrook,” said I.

“He is not at home. He is away.”

“Mrs. Estabrook.”

“She is not well, sir. She cannot see anybody.”

These conventional answers seemed to put an end to the interview: if she had not spoken again, with that strange look of apprehension and terror rising to her eyes, I would have bowed and turned away. But her voice trembled as she moved toward me timidly and said, “Will you leave a message? Will you call again? Will you say—will you say—”

Her sentence failed like that. As it did, words sprang to my mouth. I looked at her accusingly.

“Yes,” I snapped. “On the second story of the Marburys’ house there is, of course, a partition. I called to ask Mrs. Estabrook what was on her side of that wall.”

This information acted like dynamite. You would have said that it had blown to pieces some vital organ of the old servant. The color ran out of her face as if her head had lost its connection with her body.

“This is terrible,” she choked. “Oh, ’tis awful! Who are you? Who can you be? Somebody has sent you.”

She caught the edge of the door and pushed it toward me.

“I know who you are,” she exclaimed. “You are somebody that is sent by him!”

With a final shove, then, she closed the crack which had remained, the locks moved again, the light in the vestibule went out, and I was alone on the step.

Such was the success of my first attempt to find an answer to MacMechem’s question—to solve the riddle of the blue wall. But I realized, as I stood there, looking up into the gray sky of night with its wind-driven clouds, that the presence of some peculiar form of good or evil was no longer in doubt; that little Virginia, with the sensitive receptiveness of childhood, of suffering, and of her own endearing, unworldly personality, had not been wrong; that MacMechem, like a true physician, had not excluded the unknown and now was vindicated, and that there are sometimes strange affairs that baffle our feeble diagnosis of mankind....

This is merely a recital of the facts. I am not attempting to prove anything. I merely state that, as I descended the Estabrook steps and struck off into the park, the detective instinct which lies in every one of us had wakened in me. It may have been the reason for my turning around, after I had crossed the street, between the whirr and lights of two automobiles, and stood at the opening of one of the paths of the park.

The house I had just left met my scrutiny with a cold, impassive stare of its own—its look might have been the stare of the sphinx or of a good poker player. It gave no sign. My eyes traveled up to the roof, then back again to the ground, and only when my glance dropped did I see for the second time the lurking figure of the man.

“He was watching me from first to last,” said I to myself. “He probably saw my little strategy of waiting around the corner.”

Indeed, my first impulse was to walk rapidly over the way, head him off, and ask him his business; but I considered it unwise, and plunging into the shadows of the wailing trees, I walked briskly toward the distant lights that marked my district of the city.

You know, perhaps, the feeling that you are being followed. Without recognition of any definite sight or sound, you become more and more conscious of some one skulking in the shadows behind. Finally, you hear, in one of those moments when the wind catches its breath, the breaking of a twig, the disturbance among the dry leaves that have blown in drifts over the path, and you know that some one is there.

I admit freely that I felt I had involved myself in such a manner that some one wished to do me harm. If, on the other hand, he who followed sought to rob me, the situation was as bad. The park was deserted. One does not like to call for help unless certain of danger. And therefore, though I am no longer moulded for speed, I broke into a run.

I had gone but a few paces before the other discovered that I was in flight. I heard the rapid patter of his shoes behind me. In another twenty feet I heard his voice. It was not loud and it was cautious, but it reached my ears with a suggestion of extraordinary savageness.

“Stop!” it called with an oath. “I’ve got you. Stop!”

It was not a reassuring message, of course. I tried to run faster. A moment of this endeavor only showed me that my pursuer was gaining. I therefore stopped short, stepped into the heavy shadow of an evergreen, and waited for my new friend. Though it was dark I could see him as he came, and I assure you that it surprised me when I noted that the man was well-dressed and bore the appearance of respectability.

Just as he reached the spot in front of me, I saw him hesitate as if he had discovered that I was no longer running along in front of him. I knew that an encounter could not be avoided. Accordingly I sprang forward and drove my fist into his neck. Instantly I found myself grappling with him. I felt the watch in his waistcoat pocket as I pressed my knee into his stomach, and with my face near his I could see by the look in his eyes that my blow had staggered him and put him at a disadvantage. Some years ago I could deliver a heavy punch and the knack had stayed with me. I threw my weight against him once more, bore him down onto the leaves and gravel, and found myself on top.

Both of us were panting; we were breathing into each other’s faces when suddenly I saw his eyes open wide as if he had seen a vision.

“I know you now. You are the doctor!” cried he. “Stop! Tell me, for God’s sake, what’s wrong with my wife!”

“Your wife?” I cried, dumbfounded. “Who are you?”

He struggled to his feet and leered at me. His face twitched with emotion.

“I am Jermyn Estabrook,” he gasped.

You may imagine my astonishment when, after struggling with a man who had pursued me through the dark paths of the park like one who sought my life, he whom I had never seen before should now appeal to me as if I could lift him from the depths of some profound despair. He had cried out that I must tell him what was wrong with his wife. I had never so much as set eyes upon her. He had said he was Jermyn Estabrook. And though, with my face close to his, I could see that he was covered with bits of dead leaves and mud and the sweat of his desperate struggle, I felt that he told the truth.

“I have never been to your home but once in my life,” I said. “You were watching me on that occasion—to-night. That is plain. I did not go in.”

“I have made a