Harold Adler uttered a hoarse cry of warning that came just a bit too late. With one of those lightning-like movements of his, Black Hood had pulled the revolver out of McGinty's holster, turned it on the sergeant. A copper near the door started to intervene, but Black Hood stopped him with a narrow-eyed glance that held all the threat of a thunderbolt.
"Make a move toward me, and I put a bullet into McGinty's back," he said. "No one will ever see the face of Black Hood and live to talk about it. I've just given McGinty the entire solution to this mystery. I've told him that Jack Carlson was the Eye. I've explained how Jack Carlson was murdered and his powerful position in the underworld was usurped by another man who now poses as the Eye. If there is any doubt in his mind, I am about to dispel it."
Black Hood picked up the ultra-violet lamp with his left hand while his right kept the gun on McGinty. He said, "Mr. Adler, will you kindly turn out the lights."
Adler hesitated.
"Do as you're told," Black Hood insisted, "if you don't want to witness murder. And I want to warn everyone in this room, that when the lights go out if anyone makes any move toward me, McGinty will die. Even if I were to be shot, the reflex action of my fingers would pull the trigger of this revolver and McGinty will die. I am no murderer, but if you interfere with me in this business, you'll make a murderer of me."
Adler switched out the lights. The darkness lay like a smothering blanket upon them all. The air itself had a certain electrical tenseness about it, like the silence before a storm.
"I am now going to switch on the ultra-violet light. If the filter is perfect, you will not be able to see the light, because ultra-violet rays, when unadulterated by other rays, cannot be seen by the human eye. There. The light is on.
"I have offered evidence to Sergeant McGinty in which I intended to prove that Biggert, William Weedham's secretary, was killed because he was about to show to William Weedham a check to which William Weedham's signature had been forged. Not only that, but the forger, in cashing the check, also forged the endorsement of Major Paxton, to whom the check was made out.
"I have further pointed out to McGinty, that this same killer disposed of Jack Carlson, after Carlson had been betrayed by a woman. This woman must have been Carlson's friend. She must have known all his secrets, including the fact that Carlson was the Eye. She gave all this information to another man—the same man who forged the check which I mentioned before. Then she assisted this killer to shoot Carlson. This woman's face powder was treated with naphthionate of sodium. A little of this powder rubbed from her cheek to Carlson's lapel made Carlson a perfect target in pitch darkness, provided that darkness was penetrated by rays of invisible ultra-violet or black light. I have a sample of that woman's face powder here on McGinty's desk."