When the front door closed after the departing merry-makers and the sound of the last wheels died away down the avenue, the guests of the house party filed slowly up to bed. Mrs. St. Clair, at the head of the stairs, kissed each of the girls good-night and shook hands with the boys. And, as a final token of their regard, before turning in, the boys trooped from door to door, singing, “Good-night, ladies,” with Charlie accompanying on his mouth organ.

And now the house was still, and our four friends in their bathrobes were seated on the hearth rug around the wood fire in one of the bedrooms, talking in whispers, as girls will do after a party.

“Do you suppose Belle Rogers has been converted, or reformed, or something?” observed Nancy. “What else could have induced her to be so unselfish as to wear Fannie’s old dress and let Fannie wear her best one?”

“It’s the mystery of the age,” said Elinor. “And how different she seemed, too. How quiet and meek. Perhaps, after all, it was her clothes that made her haughty. Who could be anything but lowly in a faded yellow muslin?”

“She was angry at first,” put in Mary. “I saw the danger signals at dinner. But I really believe she had as good a time as any of us afterwards. Perhaps she realized that without the blue satin, she was just on a par with the rest of us, and she forgot to be conscious.”

“And how different Fannie was under the influence of the blue satin,” continued Elinor. “She talked and laughed quite loudly, and she was really rude to Belle several times. Girls, if we ever have blue satins, will they change our dispositions——”

A tap at the door interrupted the conversation, and Mrs. St. Clair, in a long lavender dressing gown, tripped into the room.

“I hope our talking hasn’t disturbed you, Mrs. St. Clair,” said Billie.

“No, no, dear, I am glad you were talking, because I had hoped to find some one of you still awake. I have come to ask a great favor. Will one of you, or all of you, go with me up in the attic for a few minutes? I should have asked one of the servants, but their lights are all out. I suppose they are sound asleep. Percy is asleep, too. I have just come from his room. He is tired out. You can’t think how hard he has worked in the last few days.”

“Let me go with you, Mrs. St. Clair,” put in Elinor.

“Let us all go,” suggested Billie.

“Very well, dear. The more of you the better. To tell the truth, I am a little worried. It’s nothing, of course; I am sure to find it, but I should like to take a look before I go to bed.”

“Have you lost something, Mrs. St. Clair?” asked Mary.

“Yes, I have lost my pearl necklace. I really never missed it until a few moments ago. I have looked downstairs everywhere, but I feel sure that I dropped it in the attic when I was dancing that ridiculous twirling waltz with Ben. It serves me right for trying to be a young girl when I am really such an old lady.”

“You are really the youngest of us all,” protested the four young girls, following her on tiptoe up the stairs into the attic.

All the members of the searching party were sure that the necklace would be found at once somewhere on the attic floor, or in the folds of the sheet or the pillow-case Mrs. St. Clair had been wearing. Yet Billie and Mary had good reason to know that robbers were at large in the village of West Haven, and the memory of the face Billie had seen in the mirror suddenly became painfully distinct.

Mrs. St. Clair lit a few gas jets in the attic and the great place seemed ghastly enough in the half light with the grotesque jack-o-lanterns grinning at them from above; the black-curtained side shows and an occasional sheet and pillow-case made a weird picture.

They searched the floor carefully, looked into the booths with candles, shook out sheets and pillow-cases, but there was no sign of the missing necklace.

“If it had only been something else,” said Mrs. St. Clair. “I should rather have lost almost anything in the world than my pearl necklace. It was a wedding present from Percival’s father and I valued it more than all my other jewelry together. I don’t see how I could have dropped it so carelessly. When we went down to supper I threw a scarf around my shoulders and that is probably why I never noticed that my pearls were gone. You were standing near me, Mary, and Belle and her friend were there, too. You don’t remember to have noticed the necklace at that time, do you? One of you helped me on with my scarf.”

Mary shook her head.

“I must ask Belle and Miss Alta to-morrow. It is so important to know whether I lost the necklace up here or below.”

“Perhaps you dropped it on the steps,” suggested one of the girls.

“If I did, it must have been trod on by many pairs of feet, then. Oh, dear, I am so sorry. Only this evening I said to myself, I must have the clasp to the necklace repaired. I had intended to take it to town next week to the jeweller’s.

“But I must not keep you up any longer. You were dear children to come up with me. Now go to bed and don’t think of it any more. I should not have been so selfish. You are all dead tired, I know, for I am myself.”

They turned and trooped downstairs again, and with softly spoken good-nights separated at their bedroom doors.

Billie and Mary were the last to enter the room they shared. They had stopped for a drink of ice water from a big glass pitcher, which had been placed with a tray of tumblers on a table at the far end of the hall. They were drinking their water silently, each absorbed in her own thoughts, when suddenly Mary grasped Billie’s hand and whispered:

“Look! On the steps!”

But Billie was looking with all her eyes before Mary had spoken.

A figure was gliding down the steps wrapped in a sheet. The stray ghost had evidently seen the girls at the same moment they had caught sight of it, for it finished the flight almost with a bound, and with a swift run disappeared through a door leading to a passage back of the steps, with Billie and Mary running behind. But the sheeted figure was too swift for them, and they heard one of the doors in the passage open and close softly just as they reached the entrance.

“It was this door,” said Mary.

“Or this one,” said Billie, pointing to the door of the room next the one Mary had chosen as the door the phantom had disappeared through.

“We’ll settle it,” said Billie. “I’ll knock on this one and you knock on that one.”

“They are the small single rooms that Belle and Fannie and Roly Poly have,” whispered Mary, as she tapped on a door.

There was no answer and she went in. It was Belle’s room and she was sleeping deeply. Mary smiled as she noticed that Belle now wore a night cap over the rubber curlers. Her cheek was pillowed on her hand and her breath came softly and regularly.

No answer came to Billie’s tap, either, and when she turned the knob she found that the door was locked. She tapped again and rattled the knob.

“Who is there?” came a sleepy voice.

“Open the door,” called Billie.

“Tell me who you are first.”

“Billie Campbell.”

Presently the door was thrown open and Fannie, with her dark hair standing out all over her head in a dishevelled mass, peered into the hall.

“What is the matter?” she asked. “The house is not on fire?”

“No, but Mary and I were in the hall and we saw some one come down from the attic and go into one of these rooms, and we thought we had better wake you up.”

“They could not have come in here,” said Fannie. “My door was locked.”

Billie looked at her curiously.

“What a little actress you are,” she thought.

“It doesn’t matter, only Mrs. St. Clair had lost something, and we were afraid a thief might be in the house. You know there have been several robberies lately in West Haven.”

Fannie gave her a long and scornful stare.

“At the High School, you mean?”

“Particularly at the High School,” replied Billie gently. Somehow, she felt a sort of contemptuous pity for this unfortunate little creature who had been taught, perhaps by poverty, to stoop to so much villainy.

“What’s all this racket about?” demanded Rosomond McLane, opening her door which was the third one along the passage and thrusting out her merry, round face.

“You didn’t hear anything did you?” asked Billie. “Mary and I thought we saw some one in a ghost dress come down this passage and go into one of these doors.”

“Good heavens! I am terrified out of my wits, I would rather it would be a burglar than a ghost. Did you really see something?”

“Forget it,” said Billie. “Go back to bed and lock your door. It was just a shadow, I suppose.”

Fannie had already locked her own door and the girls retreated to their room, somewhat crestfallen, feeling very much like two fighters who had been worsted in battle.

When they had crawled into bed and settled themselves under the covers, Billie gave a deep sigh and whispered:

“Mary, dear, which one do you think it was?”

“There is only one thing that would make me think it was Belle,” replied Mary. “If she had really been asleep, she would have waked and come out to find what was the matter. She is the most deadly curious soul alive.”

“That’s very slight evidence, Mary. She might have been specially tired to-night. Now, I believe it was Fannie. She had such a wild, dishevelled look and her door was locked. She is such a creeping, crawling little thing. Besides, I don’t believe Belle would have had the courage to go up in the attic alone.”

“Billie,” observed Mary, after a short silence, “I don’t know what it is all about, but something is going on around us. I believe that you and I, in some way, are mixed up in some kind of conspiracy. The box of jewels is in it and Fannie and Belle are in it. It’s like seeing a lot of figures moving about through a thick curtain. You know they are there, but you don’t know what they are all doing. I’m frightened, Billie, very frightened.”

Mary gave that dry sob which was just as painful as crying and much worse to hear.

Billie put her arms around her friend and tried to comfort her.

“Don’t be scared, Mary, dear. It will all come right. I have made up my mind to one thing. That is, I will not leave that unlucky box at your mother’s house any longer. We shall have to find some new place to keep it.”

Presently the two girls dropped off to slumber, and of all the sleepers in the big house, only one person heard the clock in the hall strike the passing hours. She tossed and tumbled on her bed like a boat on a restless sea, and moaned to herself. Her lace-frilled night cap had slipped, and one red rubber horn pointed upward, like an accusing finger.