After a time, with sudden determination, the young man dropped into a chair at his desk, and wrote in duplicate, on a narrow strip of tough tissue-paper, just one line: 

   Are you safe?  Is all well?  Answer quick. 
   W.

Then he mounted to the roof.  As he flung open the trap a man on the top of the house next door darted behind a chimney.  Mr. Wynne saw him clearly—­it was Frank Claflin—­but he seemed to consider the matter of no consequence, for he paid not the slightest attention.  Instead he went straight to a cage beside the pigeon-cote, wherein a dozen or more birds were imprisoned, removed one of them, attached a strip of the tissue-paper to its leg, and allowed it to rise from his out-stretched hand.

The pigeon darted away at an angle, up, up, until it grew indistinct against the void, then swung widely in a semicircle, hovered uncertainly for an instant, and flashed off to the west, straight as an arrow flies.  Mr. Wynne watched it thoughtfully until it had disappeared; and Claflin’s interest was so intense that he forgot the necessity of screening himself, the result being that when he turned again toward Mr. Wynne he found that young man gazing at him.

Mr. Wynne even nodded in a friendly sort of way as he attached the second strip of tissue to the leg of another bird.  This rose, as the other had done, and sped away toward the west.

“It may be worth your while to know, Mr. Claflin,” Mr. Wynne remarked easily to the detective on the other house, “that if you ever put your foot on this roof to intercept any message which may come to me I shall shoot you.”

Then he turned and went down the stairs again, closing and locking the trap in the roof behind him.  He should get an answer to those questions in two hours, three hours at the most.  If there was no answer within that time he would despatch more birds, and then, if no answer came, then—­then—­Mr. Wynne sat down and carefully perused the newspaper story again.

At just about that moment the attention of one John Sutton, another of the watchful Mr. Birnes’ men, on duty in Thirty-seventh Street, was attracted to a woman who had turned in from Park Avenue, and was coming rapidly toward him, on the opposite side of the street.  She was young, with the elasticity of perfect health in her step; and closely veiled.  She wore a blue tailor-made gown, with hat to match; and recalcitrant strands of hair gleamed a golden brown.

“By George!” exclaimed the detective.  “It’s her!”

By which he meant that the mysterious young woman of the cab, whose description had been drilled into him by Mr. Birnes, had at last reappeared.  He lounged along the street, watching her with keen interest, fixing her every detail in his mind.  She did not hesitate, she glanced neither to right nor left, but went straight to the house occupied by Mr. Wynne, and rang the bell.  A moment later the door was opened, and she disappeared inside.  The detective mopped his face with tremulous joy.