It was a woman's handkerchief, a tiny square of lace-edged linen, of an inexpensive variety. But it was not the mere presence of the handkerchief that so interested him. It might readily have belonged to Miss Morton herself, and have been accidentally dropped from the window. There were two things about this particular handkerchief, however, that marked it as a clue of the utmost value. One was the fact that in its corner was embroidered an initial, the letter "F." The other was that two of the corners of the handkerchief were knotted together, as though it had been tied about someone's wrist, for what reason, he could not imagine.
The latter feature puzzled the detective greatly. He could not form any hypothesis to account for it. If the Ford woman, as indicated by the presence of the handkerchief, marked with an "F," had been on the fire-escape, why were there no tell-tale marks to indicate it? And if she had not been there, why was her handkerchief found there, knotted in this peculiar way? Had it formed part of some apparatus, some device, made of a pole and a cord, for inserting the threatening letters through the window? If so, it might, of course, have become detached while the device was being used. Duvall remembered that he had not examined the fire escape on the night when the astonishing apparition had appeared beside Ruth Morton's bed, because the window opening on the fire escape had been closed and locked. Had the handkerchief been left there then? He sat for a long time in the deserted library, trying to hit upon some reasonable theory to explain the matter, but his efforts resulted in failure. Not the least confusing feature of the affair was the fact that the woman, Marcia Ford, was not the woman he was seeking. He had seen her at the studio that morning, and knew that she was not the one who had escaped from the cab the night before. Were there then two working together? If so, he would, through the Ford girl, in all probability be able to trace her confederate. He waited patiently until the waning afternoon light told him that it was time to begin his watch before the house at number 162.
Across the street a residence, closed for the summer, its front entrance boarded up, afforded him a convenient place to wait. He sat down upon the steps, and pretended to be occupied with a newspaper. His eyes, however, sought constantly the doorway opposite.
A number of persons entered the place, during the next two hours, but Marcia Ford was not amongst them. As the darkness began to approach, and lights in the streets and houses flared up, Duvall rose, crossed the street, and stationed himself at a nearer point, from which he might the more certainly identify anyone entering the house. Miss Ford, however, failed to appear.
From the sign in the window, to the effect that roomers were wanted, Duvall concluded that the Ford girl did not take her meals in the house. His watch showed him that it was nearly seven. Doubtless she had arranged to dine before returning home. In a flash it came to him that his opportunity to make an examination of her room was now at hand.
To secure entrance to the room by the usual channels was clearly out of the question. The people at the boarding house would, of course, not permit it. But could he discover the means of communication, whatever they were, between Miss Morton's apartment and the girl's room, he might be able to enter the latter unknown and unobserved. He had thought of attempting this during the afternoon, but realized that he could not hope to accomplish it, in broad daylight, without being seen by the occupants of the neighboring buildings, and perhaps arrested as a burglar or sneak thief.
With a last glance down the street, he hastened back to the apartment building and made his way to Mrs. Morton's flat. Passing quickly through Ruth Morton's bedroom, he climbed out upon the fire escape and looked about.
Below him were the rear yards of the houses fronting on the next street. To the right he could see the bulk of the apartment building, blocking his view of the avenue beyond. To the left were the rear buildings of the adjoining houses. It was quite dark, the sky was starless, but all about him gleamed the lights in the windows of the neighboring buildings.
Neither to the right, nor to the left was there any possible way by which access to the point where he now stood could be gained. From below, it was possible, although his previous examination had showed him both the fact that the newly painted surface of the fire escape was unmarred, and that the ladder at the lower floor was drawn up some nine or ten feet from the ground. He felt certain that Miss Ford had not reached Ruth's room in that way.
He glanced upward. The fire escaped stopped at the level of the floor above. To ascend from it to the roof was impossible.