"I think so. I don't generally lock it."
"And you heard no door open or close—anywhere?"
"No; none. Everything in the house was perfectly still."
"And yet you knew that some one was in the room. How was that?" Vance's voice, though gentle, was persistent.
"I—don't know . . . and yet there must have been something that told me."
"Exactly! Now try to think." Vance bent a little nearer to the troubled girl. "A soft breathing, perhaps—a slight gust of air as the person moved by your bed—a faint odor of perfume. . . ?"
She frowned painfully, as if trying to recall the elusive cause of her dread.
"I can't think—I can't remember." Her voice was scarcely audible. "I was so terribly frightened."
"If only we could trace the source!" Vance glanced at the doctor, who nodded understandingly, and said:
"Obviously some association whose stimulus went unrecognized."
"Did you feel, Miss Greene, that you knew the person who was here?" continued Vance. "That is to say, was it a familiar presence?"
"I don't know exactly. I only know I was afraid of it."
"But you heard it move toward you after you had risen and fled toward the window. Was there any familiarity in the sound?"
"No!" For the first time she spoke with em-
