"No," said Mr. Blackford, "she is younger than I am, I believe. But I have no certain knowledge of that. Anyhow, this is part of a letter written about the girl whom I have every reason to believe is my sister. And the part that is most interesting----" "Is where----" began Will. "Can't you keep still?" begged his sister. "Has 'oo dot any tandy?" and he imitated little Dodo. "Oh, take that!" and Grace passed him a caramel. "Now, let's hear what it is, Mr. Blackford." "There is a part of the letter which says this," went on Mr. Blackford, and he proceeded to read: "'You can always identify the girl because she has a most peculiar birth-mark on----'" He ceased reading. "Well, go on, please," requested Betty. "This is getting interesting." "It isn't _getting_ interesting--it's so already," declared Mollie. "Go on, please, Mr. Blackford, tell us what sort of birth-mark your sister has." "That's just the trouble," he remarked, ruefully. "I can't do it." "Why not?" Betty wanted to know. "Because, just at that point--where the description of the birth-mark, and its location, should appear--the letter is torn. A corner is gone. I have no more idea of what sort of identifying mark my sister has, than have you. It is worse than before, for I saw hope ahead of me, only to see it disappear now. "I feel sure that the girl referred to in the old letter is my sister; but how can I identify her, in case I meet her, until I know what sort of a mark she has, and where it is?" "You can't!" declared Will, positively. "And that makes it all the more tantalizing," went on Mr. Blackford. "They even--that firm I spoke of--they even had located the part of the country where it might be possible my sister was, and now to have it fail this way----" "Where did they say she might be?" asked Amy. "Somewhere up in Canada. But it is rather vague. If only that piece was not torn off the edge of the letter!" "Can't you find it somewhere?" asked Mollie. "Maybe in forwarding it the people you hired tore it by accident." "I thought of that, so I telephoned as soon as I got this letter, asking where the missing piece was. I got word back that they knew nothing about it." There was silence for a moment, while they all looked at the mutilated document Mr. Blackford held up. It showed a tear across one corner, a tear that disposed of the most vital piece of information contained on the whole paper. "That's too bad," spoke Amy, sympathetically. "Yes," agreed Mollie, as she put back a stray and rebellious lock of hair, "it spoils all your plans, I suppose, Mr. Blackford." "In a way, yes. But I'm not going to give up. I'm going to find out where they got this document from, and go there. It may have been in some old attic trunk, among some--love letters--and the missing piece may be there." "Without it you're all at sea," declared Will. "You don't know what sort of a mark to look for, nor where it might be."