Two minutes after Tom Carver entered the arcade, Imran Bell came sprinting through the gallery door. He held his brass miner’s safety gauze lamp and a wet strip of lead-acetate test paper that had turned jet-black inside its glass vial: H2S: 45 PPM · CRITICAL EXPOSURE.
“Stop Carver!” Imran shouted, lunging toward the speaking tube. “Korr! Yell down the pipe! Don’t let him enter the lower junction!”
Inspector Korr Var blew three shrill blasts into the brass whistle tube that vented into the arcade. Down in the tunnel, sixty paces away, Tom Carver stopped. Just then, his lantern beam lit up a dense, sickly yellow vapor rolling across the floorboards from a cracked sewer vault.
“Tom!” Imran shouted into the tube. “The heat shock has burst an old cesspit beneath the brewery! The gas in that lower pocket is hydrogen sulfide—forty-five parts per million! Two breaths of that will drop you dead on the flags! Back out six paces! Take the upper brick chimney pipe around the chimney arch! The air is clean up there!” Down in the tunnel, the carter’s boots splashed backward as he followed the exterminator’s directions, bypassing the invisible poison through the upper air-flow gallery. Modern detection had saved another life.
