Long after every one had retired Ruth Stuart lay wide awake. Try as she might, sleep refused to visit her eyelids. At last, after she had counted innumerable sheep and was wider awake than ever, she resolved to go and waken Bab. Ruth moved about in the dark carefully, in order not to arouse Grace, with whom she roomed, found her dressing-gown and slippers, and tip-toed softly into Barbara’s room. She knew that Barbara would not resent being awakened even at that unseasonable hour.

“Barbara, are you awake?” she whispered, coming up to Bab’s bed and laying a gentle hand on her friend’s face. “I want to talk with you and I am so thirsty. Won’t you come downstairs with me to get a drink of water?”

Bab turned over sleepily and yawned: “Isn’t there always some water in the hall, Ruth? I am so tired I can’t wake up,” she declared.

But Ruth gave her another shake. Barbara crawled slowly out of bed, while Ruth found her bedroom slippers and wrapped her in her warm bathrobe. Then both girls stole softly out into the dark hall.

At the head of the stairs there was a broad landing. On this landing, just under a stained glass window, there was a leather couch and a table, which always held a pitcher of drinking water. On the window ledge the servants were required to keep a candle, so that anyone who wished to do so might find his way downstairs at night, without difficulty.

The two girls made their way slowly to this spot, and Bab felt along the sill for the candle. It was not in its accustomed place.

“I can’t find the candle, Ruth,” Bab whispered. “But you know where to find the water. Just fumble until you get hold of the pitcher.”

“Won’t you have a glass of water?” Ruth invited, pushing the tumbler under Bab’s very nose. Then the two girls began to giggle softly.

“No, thank you,” Bab answered decidedly. “Come, thirsty maiden! Who took me from my nice warm bed? Ruth Stuart! Let’s go back upstairs and get to sleep again in a hurry.”

But for answer, Ruth drew Barbara down on the old leather couch in the complete darkness and put her arms about her.

“Don’t go back to bed, Bab. I’m not a bit sleepy. That’s why I dragged you out of bed. I couldn’t go to sleep and I just had to have company. Be a nice Bab and let’s sit here and exchange conversation.”

“All right,” Bab replied amiably, snuggling up closer to her friend. “Dear me, isn’t it cold and dark and quiet out here!”

Ruth gave a faint shiver. Then both girls sat absolutely still without speaking or moving ­they had heard an unmistakable sound in the hall below them. The noise was so slight it could hardly be called a sound. Yet even this slight movement did not belong to the night and the silence of the sleeping household.

The sound was repeated. Then a stillness followed, more absolute than before.

“Is it a burglar, Bab?” Ruth breathed.

Barbara’s hand pressure meant they must listen and wait. “It may be possible,” Bab thought, “that a dog or cat has somehow gotten into the house downstairs.”

At this, the girls left the sofa and, going over to the banister, peered cautiously down into the darkness.

This time the two girls saw a light that shone like a flame in the darkness below. Quietly there floated into their line of vision something white, ethereal ­perchance a spirit from another world. It vanished and the blackness was again unbroken. The figure had seemed strangely tall. It appeared to swim along, rather than to walk, draperies as fine as mist hanging about it.

“What on earth was that, Barbara?” Ruth queried, more curious than frightened by the apparition. “If I believed in spirits I might think we had just seen the ghost of Harriet’s mother. Harriet’s old black Mammy has always said that Aunt Hattie comes back at night to guard Harriet, if she is in any special trouble or danger.”

“I suppose we had better go downstairs and find out what we have seen,” whispered more matter-of-fact Bab. “Mr. Hamlin is not here. I don’t think there is any sense in our arousing the family until we know something more. I should not like to frighten Mrs. Wilson and Harriet for nothing.”

The two girls slipped downstairs without making a sound. Everything on the lower floor seemed dark and quiet. Ruth and Bab both began to think they had been haunted by a dream. They were on their way upstairs again, when Ruth suddenly turned and glanced behind her.

“Bab,” she whispered, clutching at Barbara’s bathrobe until that young woman nearly tumbled backwards down the steps, “there is a light in Uncle’s study! I suppose it is Harriet who is down there.”

It flashed across Bab’s mind to wonder, oddly, if Harriet’s visit to her father’s study at night could have anything to do with her debt to her dressmaker of five hundred dollars! For Mollie had reported to her sister that Harriet was feeling desperate over her unpleasant situation.

“If it is Harriet downstairs I don’t think we ought to go down,” Bab objected. “We would frighten her if we walked in on her so unexpectedly.”

“Harriet ought not to be alone downstairs,” Ruth insisted. “Uncle would not like it. I am going to peep in on her, and then make her come on upstairs to bed.”

Ruth led the way, with Bab at her heels. But it occurred to Barbara that the midnight visitor to Mr. Hamlin’s study might be some one other than his daughter. Bab did not know whether Mr. Hamlin kept any money in his strong box in the study. She and Ruth were both unarmed, and might be approaching an unknown danger. Quick as a flash Bab arranged a little scheme of defense.

There were two old-fashioned square stools placed on opposite sides of the hall. Without a word to Ruth, who was intent on her errand, Bab drew out these two stools and placed them side by side in the immediate centre of the hall. Any one who tried to escape from the study would stumble over these stools and at once alarm the household. Of course, if Bab and Ruth found Harriet in her father’s study Bab could warn them of her trap.

“What shall we do, Bab?” Ruth asked when Barbara joined her. “The light is still shining in the study. But I do not want to knock on the door; it would frighten Harriet. And it would terrify her even more if we walked right into the study out of this darkness. But we can’t wait out here all night. I am catching cold.”

Barbara did not reply. They were in a difficult situation. Suppose Harriet were in the study? They did not wish to frighten her. In case the veiled figure was not Harriet any speech of theirs would give their presence away.

“I think we had better open the door quickly and rush in,” Ruth now decided. “Then Harriet can see at once who we are.”

Without waiting for further consultation with Bab, Ruth flung wide the study door.

In the same instant the light in the room went out like a flash.

“Harriet, is that you?” Ruth faltered. There was no answer, save some one’s quick breathing. Ruth and Bab could both perceive that an absolutely white figure was crouched in a corner of the room in the dark.

Bab moved cautiously toward the spot where she knew an electric light swung just above Mr. Hamlin’s desk. But it was so dark that she had to move her hand gropingly above her head, for a moment, in order to locate the light.

The veiled being in the corner must have guessed her motive. Like a zephyr it floated past the two girls. So light and swift was its movement that Bab’s hand was arrested in its design. Surely a ghost, not a human creature, had passed by them.

The next sound that Ruth and Bab heard was not ghostlike. It was very human. First came a crash, then a cry of terror and surprise.

At the same moment Bab found the light she sought, turned it on, and Ruth rushed out into the hall.

There on the floor Ruth discovered a jumble of stools and white draperies. And, shaking with the shock of her fall and forced laughter, was ­not Harriet, but her guest, Mrs. Wilson! She had a long white chiffon veil over her head, a filmy shawl over her shoulders, and a white gown. With her white hair she made a very satisfactory picture of a ghost.

“My dear Mrs. Wilson!” cried Ruth, in horrified tones, “What has happened to you? Were you walking in your sleep! Do let me help you up. I did not know these stools were out here where you could stumble over them.”

Bab stood gravely looking on at the scene without expressing such marked surprise.

Mrs. Wilson gave one curious, malignant glance at Bab, then she smiled:

“Help me up, children. I am fairly caught in my crime.”

Bab took hold of Mrs. Wilson by one arm, Ruth grasped her by the other, and they both struggled to lift her. Mrs. Wilson gave a slight groan as she got fairly on her feet. Her right hand clutched Bab for added support. In falling over the stools Mrs. Wilson had given her knee a severe wrench.

At the moment she staggered, Barbara saw a large, oblong envelope fall to the floor from under Mrs. Wilson’s soft white draperies.

“What is the trouble?” called Harriet, Mollie and Grace, poking their three sleepy heads over the banisters.

At this interruption Bab stooped down and quickly caught up the envelope, while Mrs. Wilson’s attention was distracted by the three girls who were rapidly descending the steps.

“Mrs. Wilson came downstairs for something,” Ruth explained in her quiet, well-bred fashion. “Bab and I heard a noise and, as we did not recognize her, we followed her. We frightened Mrs. Wilson so that she stumbled over these stools out in the hall. I am afraid she is a little hurt. I think you had better call the servants, Harriet.”

Ruth did not, for an instant, let the surprise she felt at Mrs. Wilson’s extraordinary conduct appear in her voice.

“No, don’t call any of the servants to-night, Harriet,” Mrs. Wilson demurred. “I am all right now. I owe you children an apology for my conduct to-night and also an explanation. But I think I can explain everything much more satisfactorily if we wait until morning. I think Miss Thurston already understands my escapade. I have taken her into my confidence.”

Mrs. Wilson directed at Barbara a glance so compelling that it was almost hypnotic.

Bab did not return her look or make any answer.

A little while later Barbara disappeared. She went back alone to Mr. Hamlin’s study. On top of his desk she discovered a box about a foot and a half long. It had been opened and a key was lying beside it on the desk. Barbara could see that there was no money in the box, only a collection of papers. Bab returned the long envelope, which she had found at Mrs. Wilson’s feet in the hall to its place, turned the key in the lock of the box, and then carried the key upstairs, intending to hand it over to Harriet. But Bab did not know whether or not she ought to explain to Harriet how she had come by the key.

Harriet was in the room with Mrs. Wilson, seeing her guest to bed for the second time, when Barbara went upstairs. Bab had no desire to face Mrs. Wilson again that night. The distrust of the woman that was deepening in the girl’s mind was too great to conceal.

“Come into my room in the morning before breakfast, Harriet, dear,” Mrs. Wilson entreated, as she kissed her young hostess good night. “I know you will forgive my foolishness, when I have had a little talk with you. It is too late now for explanations.”

It was between two and three o’clock in the morning before the household of the Assistant Secretary of State again settled itself to sleep. Under her pillow Barbara Thurston had the key to Mr. William Hamlin’s strong box, in which valuable state papers were sometimes temporarily placed.