Sturgis, taking up his lighted candle, made his way to the door of the subterranean passage and tried in vain to open it; the heavy iron bolt remained immovable in its socket. Inch by inch he scrutinized the door with growing anxiety. At last he abandoned the search, and returned in the direction of the square chamber. "That explains why he wanted to shut me in here when I was in his office," he muttered under his breath. "What is the matter?" asked Sprague. "We are caught like rats in a trap," replied Sturgis. Then with feeling he added: "I do not know how this will end, old man. I have bungled and I fear the game is lost. If our lives are the forfeit, you will owe your death to my stupidity." Sprague looked at his friend, as if surprised to hear him apparently abandon the fight. "Don't worry about me," he said kindly; "I came here of my own free will. But," he added, as a vision of Agnes Murdock flashed upon his mind, "I have no intention to die just yet, if I can help it. Are we not both able-bodied men and armed? What can one man do against two?" "It is not an open fight," said Sturgis, "but I am glad to see your spirit. I do not give up; but I want you to realize that we are in a critical situation, with the odds enormously against us." "Why, what can Murdock do?" "Perhaps what he did to Chatham. It will probably not be long before we discover what that was." "But there must be some way of opening that door from the inside," said Sprague. "There evidently is none," replied Sturgis; "he probably controls these doors from the outside by electrical connection." The men were back in the square chamber. Sturgis's eyes were roving restlessly over the walls, ceiling and floor in search of a loophole of escape. "There is no chance to reach the skylight without a ladder; and even if we could reach it, we should be no further advanced, as it would be impossible to make any impression on the steel shutters. That leaves the register and the speaking-tube. While I examine the register, suppose you try the tube. If it connects with the Manhattan Chemical Company's office, there is a bare chance that we may attract the attention of the detectives whom we left there." "As we were saying, Mr. Sturgis----" The words came in Murdock's mocking tones. Sturgis quickly held the lighted candle above his head and peered in the direction whence came the sound. A panel of the door at the head of the stairs had been pushed up, revealing a small opening covered by a strong and closely woven wire netting. "As we were saying, 'murder will out!' Nevertheless, it is sometimes easier to weld a chain, even of circumstantial evidence, than it is to predict who will be bound in it." Sturgis and Sprague stood in the glimmering light of the candle, silently watching the glowing eyes behind the screen.