The Doctor watched her go—­saw the door close behind her.  Instantly his face set into tense and wary lines.  He glanced about—­then ran lightly into the alcove and noiselessly unfastened the bolt on the terrace door which he had pretended to fasten after his search of the shrubbery.  When Dale returned with the matches, he was back where he had been when she had left him, glancing at a magazine on the table.

He thanked her urbanely as she offered him the box.  “So sorry to trouble you—­but tobacco is the one drug every Doctor forbids his patients and prescribes for himself.”

Dale smiled at the little joke.  He lit his cigarette and drew in the fragrant smoke with apparent gusto.  But a moment later he had crushed out the glowing end in an ash tray.

“By the way, has Miss Van Gorder a revolver?” he queried casually, glancing at his wrist watch.

“Yes—­she fired it off this afternoon to see if it would work.”  Dale smiled at the memory.

The Doctor, too, seemed amused.  “If she tries to shoot anything—­ for goodness’ sake stand behind her!” he advised.  He glanced at the wrist watch again.  “Well—­I must be going—­”

“If anything happens,” said Dale slowly, “I shall telephone you at once.”

Her words seemed to disturb the Doctor slightly—­but only for a second.  He grew even more urbane.

“I’ll be home shortly after midnight,” he said.  “I’m stopping at the Johnsons’ on my way—­one of their children is ill—­or supposed to be.”  He took a step toward the door, then he turned toward Dale again.

“Take a parting word of advice,” he said.  “The thing to do with a midnight prowler is—­let him alone.  Lock your bedroom doors and don’t let anything bring you out till morning.”  He glanced at Dale to see how she took the advice, his hand on the knob of the door.

“Thank you,” said Dale seriously.  “Good night, Doctor—­Billy will let you out, he has the key.”

“By Jove!” laughed the Doctor, “you are careful, aren’t you!  The place is like a fortress!  Well—­good night, Miss Dale—­”

“Good night.”  The door closed behind him—­Dale was left alone.  Suddenly her composure left her, the fixed smile died.  She stood gazing ahead at nothing, her face a mask of terror and apprehension.  But it was like a curtain that had lifted for a moment on some secret tragedy and then fallen again.  When Billy returned with the front door key she was as impassive as he was.

“Has the new gardener come yet?”

“He here,” said Billy stolidly.  “Name Brook.”

She was entirely herself once more when Billy, departing, held the door open wide—­to admit Miss Cornelia Van Gorder and a tall, strong-featured man, quietly dressed, with reticent, piercing eyes —­the detective!

Dale’s first conscious emotion was one of complete surprise.  She had expected a heavy-set, blue-jowled vulgarian with a black cigar, a battered derby, and stubby policeman’s shoes.  “Why this man’s a gentleman!” she thought.  “At least he looks like one—­and yet—­ you can tell from his face he’d have as little mercy as a steel trap for anyone he had to—­catch—­” She shuddered uncontrollably.