A rubber stamp, he noted mentally, and braced himself for the pain which would follow. It came, the rapid pricking of a thousand needles, and he winced. Then the grip on his hand relaxed and he withdrew it, to look wonderingly on the blurred design of ink and blood that the tattooer had left.

    "Don't wipe it," said a muffled voice from the darkness of the hut. "Now you may come in."

    The shutter closed and was bolted. Then came the snick of a lock turning and the door opened. Genter went into the pitch-black darkness of the hut and heard the door locked by the unseen occupant.

    "Your number is K 971," said the hollow voice. "When you see that in the personal column of The Times, you report here, wherever you are. Take that…"

    Genter put out his hand and an envelope was placed in his outstretched palm. It was as though the mysterious Frog could see, even in that blackness.

    "There is journey money and a map of the district. If you spend the journey money, or if you fail to come when you are wanted, you will be killed. Is that clear?"

    "Yes."

    "You will find other money—that you can use for your expenses. Now listen. At Rochmore, 17 Park Avenue, lives Hallwell Jones, the banker—"

    He must have sensed the start of surprise which the recruit gave.

    "You know him?"

    "Yes—worked for him years ago," said Genter. Stealthily, he drew his Browning from his pocket and thumbed down the safety catch.

    "Between now and Friday he has to be clubbed. You need not kill him. If you do, it doesn't matter. I expect his head's too hard—"

    Genter located the man now, and, growing accustomed to the darkness, guessed rather than saw the bulk of him. Suddenly his hand shot out and grasped the arm of the Frog.

    "I've got a gun and I'll shoot," he said between his teeth. "I want you, Frog! I am Inspector Genter from police headquarters, and if you resist I'll kill you!"

    For a second there was a deathly silence. Then Genter felt his pistol wrist seized in a vice-like grip. He struck out with his other hand, but the man stooped and the blow fell in the air, and then with a wrench the pistol was forced out of the big man's hand and he closed with his prisoner. So doing, his face touched the Frog's. Was it a mask he was wearing?…The cold mica goggles came against his cheek. That accounted for the muffled voice…

    Powerful as he was, he could not break away from the arms which encircled him, and they struggled backward and forward in the darkness.

    Suddenly the Frog lifted his foot, and Genter, anticipating the kick, swerved round. There was a crash of broken glass, and then something came to the detective—a faint but pungent odour. He tried to breathe, but found himself strangling, and his arms fell feebly by his side.

    The Frog held him for a minute, and then let the limp figure fall with a thud to the ground. In the morning a London police patrol found the body of Inspector Genter lying in the garden of an empty house, and rang for an ambulance. But a man who has been gassed by the concentrated fumes of hydrocyanic acid dies very quickly, and Genter had been dead ten seconds after the Frog smashed the thin glass cylinder which he kept in the hut for such emergencies as these.

    

    

IV - ELK

    

    

    There was no detective in the world who looked less like a police officer, and a clever police officer, than Elk. He was tall and thin, and a slight stoop accentuated his weediness. His clothes seemed ill-fitting, and hung upon rather than fitted him.