"Oh!" she laughed, catching the look of puzzlement on the girl's face, "I haven't told you what it is. Well, my dear, it's an old woman's whim. Every so often I break loose this way and keep my memory green as one who, in her day, never entertained but in some unique fashion. I was once famous for that sort of thing, but of late years I haven't exerted myself except when bored to extinction by the deadly commonplace amusements most people offer us.
"For some time I've had this in mind, and everything prepared; you may, if you like, call it a spontaneous masquerade by moonlight. Half the fun of such affairs comes of the last-moment, makeshift costumes; if you give people much time to think them up it is always a stiff and frigid function. Moreover, it demands a perfect night--and we can't count on our Island weather twenty-four hours in advance. But to-day is perfect, and to-night will be fair with the moon at its full. You may dance on the veranda or make love on the terrace, just as you please, from ten o'clock till three--or later. Supper will be served from midnight on. At one we shall unmask.
"As I say, all preparations had been made, weather permitting; I had merely to telephone the caterers, electricians, and musicians, and scribble these invitations. I'd advise you to arrange your day to include a good long nap before dinner, for you'll be up till all hours very likely. I fancy I can promise you some fun."
Mrs. Gosnold ceased upon a note of mischievous enjoyment in anticipation that would have suited a girl of sixteen, then analysed the trouble behind Sally's perturbed countenance.
"As for your costume, you're not to give it a thought! I have arranged for it to be brought to your room at half past nine, and I pledge you my word you'll find it becoming. I have only two requests to make of you: that you refrain from unmasking or admitting your identity until one o'clock, and that if you recognise me, you hold your tongue. Is it a bargain?"
"You're so good to me," said Sally simply, "I can't think how to thank you."
"Leave that, too, to me. It's quite possible I may suggest a way." Mrs. Gosnold smiled curiously as at a thought reserved. "Now run along--order the car and put on your prettiest hat. But a moment!"
She illustrated the process of taking thought by puckering her brows and clipping her chin between a thumb and forefinger.
"Let me see. Have I remembered everybody?" She conned, half aloud, a list of names. "But no! What an oversight! I should never have forgiven myself--or have been forgiven. And my fountain pen needs refilling. No"--as Sally offered to take the pen--"sit there at the desk and write at my dictation. I will sign it."
Obediently Sally took her place at the escritoire, arranged a sheet of the monogrammed note-paper used by Mrs. Gosnold for correspondence with personal friends (as distinguished from the formal letter-head of Gosnold House, with its bristling array of telephone numbers and telegraph, post-office, railroad and steamboat addresses), dipped a pen, and waited with a mind preoccupied by visions of the night to come. Her first ball! Her first real function in Society!