Gaston led me along its edge for a hundred yards, until the wall hung over us just beyond the circle of light from the guard tower. I could see a fellow with a burp gun leaning against a post on top of the tower, looking down onto the street inside the wall. There were two large floodlights beside him, unlit. Gaston leaned close to my ear. "It kind of stinks," he said, "but the wall is pretty rough, so I think we can make it OK." He slid over the edge, found a foothold, and disappeared. I slid down after him, groping with my foot for a ledge. The wall was crudely laid, with plenty of cracks and projecting stones, but slimy with moss. I groped along, one precarious foot at a time. We passed the place where the light gleamed on the black water below, hugging the shadow. Then we were under the wall, which arched massively over us. The sound of trickling water was louder here. I tried to see what was going on ahead. Gaston had stopped and was descending. I could barely make out his figure, knee-deep in the malodorous stream. I moved closer. Then I saw the grating. It was made of iron bars, and completely blocked the passage. I climbed over to the grating, leaned against the rusty iron to ease my arms. The defense system didn't have quite the hole in it we thought it had. Gaston moved around below me, reaching under the surface to try to find a bottom edge. Maybe we could duck under the barrier. Suddenly I felt myself slipping. Below me, Gaston hissed a curse, scrabbled upward. My grip was firm, I realized in an instant; it was the grating that was slipping. It dropped another eight inches with a muffled scraping and clank, then stopped. The rusty metal had given under our weight. The corroded ends of the bars had broken off at the left side. There wasn't room to pass, but maybe we could force it a little further. Gaston braced himself against the wall and heaved. I got into position beside him and added my weight. The frame shifted a little, then stuck. "Gaston," I said. "Maybe I can get under it now, and heave from the other side." Gaston moved back, and I let myself down into the reeking water. I worked an arm through, then dropped down waist deep, chest deep, pushing. The rough metal scraped my face, caught at my clothing; but I was through. I crawled back up, dripping, and rested. From the darkness behind Gaston I heard a meshing of oiled metal parts and then the cavern echoed with the thunder of machine gun fire. In the flashing light I saw Gaston stiffen against the grating and fall. He hung by one hand, caught in the grating. There were shouts, and men dropped onto the stone coping at the culvert mouth. Gaston jerked, fumbled his pistol from his blouse. "Gaston," I said. "Quick, under the bars...." I was helpless. I knew he was too big.