I saw Hudson, the senior screw, making his way across the yard. Suddenly there was a sharp crack and a billow of dense white smoke erupted from the ground. There were more explosions in the yard and the smoke grew thick and heavy.
Hudson was now behind me, and I heard his anguished bellow. "Escape! Escape! Sound the alarm."
I looked up and saw something like the head and neck of a prehistoric monster looming through the smoke. Four knotted ropes were dangling from a steel platform. I made frantic leap and grabbed one of the ropes, my shoulder muscles cracking until I could grasp the edge of the platform. And as I looked down I saw the barbed wire apparently moving away underneath as the great articulated arm swept me over the wall...