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.