"Well, I'm going to hide this pin, right now," said Iris, "and I want you all to see where I put it. I'm afraid to put it in the bank or in Mr. Chapin's safe, for those people would get it somehow. But here are only Mr. Chapin and Mr. Hughes and Miss Darrel and myself. We are all trustworthy, and I'll hide it. Then, I shall devote my life to the solving of the mystery of the pin and Aunt Ursula's death--for, I think they are very closely connected." "I believe you!" cried Hughes, "and I agree that the best place to hide the thing is in this house. Where, now?" "In Auntie's room," said Iris, solemnly, and she led the way to Ursula Pell's sitting room. "This place is barred and we can lock the door to the other room, and keep it locked. See, I shall put it in this big easy chair, that Auntie loved to sit in. I'll tuck it well down in between the back and the seat upholstery, and no one can find it. Then, if we ever discover wherein its value lies, we know where the pin is, and can get it." "I suppose that's all right," said Mr. Chapin, a little dubiously, "but in a safe----" "No, Miss Clyde's idea is best," asserted Hughes. "How cleverly she hid the thing in her skirt hem, didn't she? Let her alone for the right dope about this. As she says, we four know where it is, and that's all that's necessary. I believe the people who want this pin will stick at nothing, and if it's in any ordinary safe they'll get it." "But what _could_ they want of it?" repeated Lucille, plaintively. "Just as a surmise, what _could_ they want of it?" "I'll tell you!" cried Iris, with a flash of inspiration. "It's a clue or a key to where the jewels are hidden! Oh, it must be! That's why they want it!" "Clue? How?" said Lucille, in bewilderment. "I don't know, but, say, the pin is the length of--of----" "I don't know what you're getting at," said Chapin, "but all pins are the same length." "What!" cried Hughes, "indeed they're not!" "Oh, well, I mean there are only a few lengths. The pins that girl took from Iris to-day are just the same as this one, aren't they?" "About," said Iris; "of course, pins differ, but the ones we use are generally of nearly the same length. But I'm sure the length or weight of this pin----" "Weight!" exclaimed Hughes; "suppose a certain weight, goldsmith's scales, you know--would open a delicately adjusted lode on a safe----" "You're romancing, man," and Mr. Chapin smiled, "but it does seem that the pin must have some significance. It would be just like Ursula Pell to call it a valuable pin, when it really was a valuable pin, in some such sense as a key to a hiding-place." "But how?" repeated Lucille; "I don't see how its weight or length could be a key----"