When once he had Chick and Marcos outside in safety, he would go after Solado and Miguel. He was resolved, too, that they would not get away this time. Later, he would lay a trap for Dugan and his gang, and thus clean up the whole job in a neat and expeditious way, and without the expenditure of very much labor. Probably Nick Carter would have carried out his plans exactly as he had planned them, but for an unforeseen accident. As he turned to go away from the place where he had been standing on the stairs, listening to the edifying conversation below, he chanced to lean rather hard against the banister. With a loud crack, it gave way. The detective, losing his balance, turned a complete somersault to the room below, landing on his head and shoulders on the table. The table collapsed under his weight; the lamp smashed--fortunately, going out, instead of blowing up--and Nick Carter, stunned, and for the moment helpless, felt himself rudely grasped by somebody and tumbled in a heap down a steep flight of stairs. When he reached the bottom he was quite unconscious. CHAPTER VI. HOW PATSY BROKE IN. The blow on the head, suffered by the detective when he fell to the table, had been a severe one, and, aggravated by another tumble when the table crumpled up beneath him, it had inflicted worse injuries than might have been thought by any one who had seen the catastrophe. It was hours before Nick Carter came to himself. When he did, he was in pitch-darkness, and he realized, from the peculiar, damp smell, that he was in a cellar. Also, he caught a pungent odor, which he recognized, and which reminded him of the conversation he had heard just before he plunged through the broken banister. “Ammonia, as sure as I am here,” he muttered. “I’ll have to move quickly, for it seems to me as if the stuff has been disturbed lately. If it has, probably it means----” The thump of an engine made him pause. “The fiends! They are generating the ammonia gas, and, of course, they will set it free by opening some of the valves, and then----” The smell of ammonia waxed stronger, and his breath began to come with difficulty. He fumbled along the rough stone wall, damp with the ooze of the marsh, until he came to an iron tank, from which the fumes were emerging so strongly that he reeled away, half suffocated. “This won’t do. They’ll get me like a stray dog in a gas chamber if I don’t find my way out.” The thumping of the engine continued, and his sense of direction told him that it was against the wall in which was a heavy door. “There is a pump and it works underneath the tank in some way,” muttered Nick. “I can’t get at it on this side. The only chance would be to get to the other room, and the door is too heavy to be broken down in a hurry. I have no tools, and----” “Gee! That’s a bum smell!” It was Patsy Garvan’s voice, almost at his ear. “Patsy!” he cried. “Chief! Where are you?” “In the cellar. Get in, quickly!”