“No sooner had I made sure of my discovery than I set out for No. 5 Oak Street, the address given by Rizzi.  There was no such person there, nor had there been anyone of that name in the house during the three years of the present tenant’s occupancy.  I went to 15 Staniford Place with the same result.  A young woman about twenty-five years of age came to the door.  She informed me that she had been born in the house and had always lived there.  She had never known anyone by the name of Weltz.  This was just what I had expected.  The man for whom we are searching is shrewd almost beyond belief, and if we succeed in finding him it will not, we may be assured, be the result of any bungling on his part.

“I have now told you all I have learned, or rather all that is sufficiently definite to communicate—­it is not much, yet it is a clue and may serve to give our hope a new lease of life.  What do you think of it, Miss Darrow?”

“I think what you have learned,” Gwen replied, “will be of the utmost importance.  You have now something definite to guide you.  I am most fortunate in having the services of such a detective, —­indeed, I am at a loss to know how to thank you for all you have done,—­for all you are doing, I—­”

“My dear Miss Darrow,” Maitland interrupted, “I need no thanks.  Be assured I am selfish in all I do.  It is a pleasure to me, therefore I do it.  You see I deserve no credit.  If I am able to free you from the danger of sacrificing yourself, I shall be more than repaid.”

Gwen made no reply, but I, sitting as I did close beside her, saw the moisture gather between her drooping lids.  Maitland took his leave almost immediately, having, he said, a long evening’s work before him; while Gwen, Alice, and I discussed the news he had brought us, until far into the night.  I did not see him the next day, which was Tuesday, and I believe not on Wednesday.  It was Thursday afternoon, if I do not mistake, that he sent me a note asking me to call on him at his office.  I went at once, thinking it might be something very important.  I found him alone and waiting for me.

“I wanted,” he began as soon as I was seated, “to talk this matter over with you.  You see the great difficulty which besets me in this case is that nearly all our evidence, while it is of a nature to enable us to convict our man once we have him, is yet of almost no assistance to us in finding him.  What do we know of him up to date; or at least of what do we feel reasonably assured?  Let us see.  John Darrow was poisoned in some mysterious way by a man who was stationed just outside the partly opened window.  The weapon, or whatever was used as such, was taken away by the murderer.  Nothing in the nature of a projectile could have been employed, since the wound was upon a part of the victim’s throat known to have been turned away from the window and to have been completely shielded upon that side by the high and massive back of the chair in which the victim sat.