And when her envelope was handed her and she had lifted the flap and withdrawn an oblong correspondence-card bearing the monogram A-G and nothing else, the final effect of meaningless mystery seemed to have been consummated. But this, as it happened, was coincident with the arrival of the last two guests--one of whom was a lithe and shapely Harlequin in party-coloured tights, and the other a bewitchingly blond Columbine-- and then the purpose of the meeting was soon exposed. With no more expression than she had employed in the case of Sally, Mrs. Gosnold saluted the last comers with a request to enter and be seated, then directed her maid to go out into the hall, close the door, and stand guard to prevent eavesdropping. When the door was closed she plunged directly into a prepared address. "I owe every one an apology," she began with a fugitive, placating smile, "for all this inconvenience and nonsense--as it must seem. But I'm sure you will bear with me when you know the circumstances, which are extraordinary, and my motive, quite a natural one. "We are now," she pursued with a swift glance that embraced the room, "just twenty-three, including myself; that is to say, everybody who slept here last night, and one or two more. And your masks are a sure screen for any betrayal of emotion when I tell you why I have asked you to oblige me by meeting here. So please retain them whatever happens." She paused, made a little gesture of deprecation. "I would rather almost anything than be obliged to say what I must. "One of us," she announced deliberately, "is a thief. These rooms were entered some time last night, while I was asleep, and all my personal jewelry was stolen. Please no one interrupt. I will answer all the natural questions before I finish. "The robbery was not difficult to accomplish." "The Island is well-policed, there has not been a burglary in its history, and I am a careless old woman. When I take my things off at night I leave them on my dressing-table. Marie, my maid, puts them away in the morning. I have three large jewel-cases, none of which is ever locked except when I travel. I have never had a safe. The jewel-cases are stored away in unlocked dresser-drawers. My bedroom and boudoir doors are never locked. And I am a sound sleeper. There is--and was--nothing to prevent the thief from entering after I had turned out my light and, employing ordinary discretion, helping him or her self. Which is precisely what happened last night. Every piece of jewelry was taken from my dressing-table, and the three jewel-cases from their drawers."