An expression of surprise and apprehension came over his face.

He glanced swiftly at Dale—­was she watching him?  No—­she sat in her chair, musing.  He turned back toward the stairs and made a frantic, insistent gesture—­“Go back, go back!” it said, plainer than words, to—­Something—­in the darkness by the head of the stairs.  Then his face relaxed, he gave a noiseless sigh of relief.

Dale, rousing from her brown study, turned out the floor lamp by the table and went over to the main light switch, awaiting Miss Cornelia’s signal to plunge the room in darkness.  The Doctor stole, another glance at her—­had his gestures been observed?—­apparently not.

Unobserved by either, as both waited tensely for Miss Cornelia’s signal, a Hand stole through the broken pane of the shattered French window behind their backs and fumbled for the knob which unlocked the window-door.  It found the catch—­unlocked it—­the window-door swung open, noiselessly—­just enough to admit a crouching figure that cramped itself uncomfortably behind the settee which Dale and the Doctor had placed to barricade those very doors.  When it had settled itself, unperceived, in its lurking place—­the Hand stole out again—­closed the window-door, relocked it.

Hand or claw?  Hand of man or woman or paw of beast?  In the name of God—­whose hand?

Miss Cornelia’s voice from the head of the stairs broke the silence.

“All right!  Put out the lights!”

Dale pressed the switch.  Heavy darkness.  The sound of her own breathing.  A mutter from the Doctor.  Then, abruptly, a white, piercing shaft of light cut the darkness of the stairs—­horribly reminiscent of that other light-shaft that had signaled Fleming’s doom.

“Was it here?” Miss Cornelia’s voice came muffledly from the head of the stairs.

Dale considered.  “Come down a little,” she said.  The white spot of light wavered, settled on the Doctor’s face.

“I hope you haven’t a weapon,” the Doctor called up the stairs with an unsuccessful attempt at jocularity.

Miss Cornelia descended another step.

“How’s this?”

“That’s about right,” said Dale uncertainly.  Miss Cornelia was satisfied.

“Lights, please.”  She went up the stairs again to see if she could puzzle out what course of escape the man who had shot Fleming had taken after his crime—­if it had been a man.

Dale switched on the living-room lights with a sense of relief.  The reconstruction of the crime had tried her sorely.  She sat down to recover her poise.

“Doctor!  I’m so frightened!” she confessed.

The Doctor at once assumed his best manner of professional reassurance.

“Why, my dear child?” he asked lightly.  “Because you happened to be in the room when a crime was committed?”

“But he has a perfect case against me,” sighed Dale.