temperature was exactly what would have been apparent if a square-shaped freezing unit had been built into the structure. The plaster was rotten from long soaking. Coghlan took out a pocket-knife and dug carefully into it.
"What rational connection can this have with that stuff in the book, and with somebody trying to kill Mannard?" he demanded as he worked.
"No rational connection," admitted Ghalil. "A logical one. In police work one uses reason oneself, but does not expect it of events."
An irregularly shaped patch of wetted plaster cracked and came away. Coghlan looked at it and started.
"Ice!" he said sharply. "There must be some machinery here!"
The space from which the plaster had come was white with frost. Coghlan scraped at it. A thin layer of ice, infinitesimally thin. Then more wet plaster, which was not frozen. Coghlan frowned. First ice, then no ice--and nothing to make the ice where the ice was. A freezing coil could not work that way. Coldness does not occur in layers or in thin sheets. It simply does not.
Coghlan dug angrily, stabbing with the point of the knife. The knife grew very cold. He wrapped his handkerchief about it and continued to dig. There was wetness and rotted plaster for another inch. Then the heavy stone wall of the building.
"The devil!" he said angrily. He stood back and stared at the opening.
There was silence. He had made a hole through rotted plaster, and found nothing but a thin layer of ice, and then more rotted plaster. He looked at it blankly. Then he saw that though the frost had been cut away, there was a slight mist in the opening he had made. He blew his breath into the hole. He made an astonished noise.
"When I blew my breath there, it turned to fog when it went through the place where the plaster layers joined!" His tone was unbelieving.
"There is refrigeration?" asked Ghalil.
"There's nothing!" protested Coghlan. "There's no possible explanation for a cold space in the middle of air!"
"Ah!" said the Turk in satisfaction. "Then we progress! Things which are associated with the same thing are associated with each other. This associates with the impossibility of your fingerprints and your handwriting and the threat to Mr. Mannard!"
"I'd like to know what does this trick!" said Coghlan, staring at the hole. "The heat's absorbed, and there's nothing to absorb it!"
He unwrapped his handkerchief from the knife, and scrubbed the cloth at the wall until a corner was set. He poked the wetted cloth into the hole he'd made. A moment later he pulled it out. There was a narrow, perfectly straight line of ice across the wetted linen.
"There's never been a trick like this before!" he said in amazement. "It's something really new!"
"Or extremely old," said Ghalil mildly. "Why not?"
"It couldn't be!" snapped Coghlan. "We 

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