"This child must go to bed now," said Lucille Darrel, with an affectionate glance at Iris. "She's had enough to upset any ordinary set of nerves, and she must rest." "Yes, Miss Clyde, go now, and I think, if you leave the pin with me I'll keep it safely, and moreover, to-morrow morning, I'll tell you its secret." "Oh, tell me now! Please do, Mr. Stone. What can it be that makes it a key to the jewels' hiding-place?" "Not to-night. Indeed, I don't yet know its secret myself, but I hope to find it out. If I may, I'll stay alone in Mrs. Pell's sitting-room for a time, until I puzzle it out." Iris reluctantly went off with Lucille, and the detective locked himself in the room where Mrs. Pell had met her tragic death. He had, as his working implements, the pin, a strong magnifying glass, a thick pad of paper and a lead pencil. As the first streaks of dawn began to show in the eastern heavens, Fleming Stone had, as results of his night's work, forty or fifty scribbled pages of the pad, all of which were in the waste basket, a small, remaining stub of lead pencil and the pin and the magnifying glass. Also he had a heavy heart and a feeling of despair and dejection. He went to his room for a few hours' sleep before breakfast time and when he met the family at table, he said shortly, "Finding a needle in a haystack is child's play compared to the task ahead of us." He refused to explain until after breakfast, and then, Iris and Lucille went with him to the sitting room and the door was closed upon them. Fibsy was there, too, as the boy was never excluded from important conferences. Stone locked the door, and then said, impressively, "The dime and pin bequeathed you by your aunt, Miss Clyde, form a far more valuable inheritance than any diamond pin I have ever seen. I congratulate you on the possession of the pin, and I ask you where the dime is." "Gracious, I don't know," replied Iris. "I threw it out of the window the day I received it, and I've never thought of it since." "The pin is a key to the hiding-place of the jewels, as I will explain fully in a few minutes," Stone proceeded, "but it may be necessary to recover the dime also, before we can utilize the information given us by the pin." Iris looked bewildered, but repeated her statement as to the whereabouts of the dime. "And again," Stone said, "the dime may be of no importance in the matter. I'm inclined to think it is not, because Pollock--or Young rather--made no effort to gain possession of the dime, did he?" "No; I think not. That first day he called on me, as Mr. Pollock, and wanted the pin, I told him he might search the lawn for the dime if he chose, but I don't think he did so." "I'll find the dime if it's out in the side yard," Fibsy volunteered. "Now, I'll tell you what this pin is," resumed Stone, holding up the mysterious bit of brass. "It contains a cipher--a cryptogram." "How can it?" asked Iris, blankly.