He chuckled and, resuming his mask, returned to his work, ignoring the two men as though they had no existence. "A little mad, old Castelli," said Milsom, "that's his one little piece--what crooked thing has he done?" "None that I know," said the other carelessly; "he lost his wife and two daughters in the Messina earthquake. I picked him up cheap. He's a useful chemist." They walked from bench to bench, but van Heerden's eyes continuously strayed to the door, behind which he pictured a caged Stanford Beale, awaiting his doom. The men were beginning to depart now. One by one they covered their instruments and their trays, slipped off their masks and overalls and disappeared through the door, upon which van Heerden's gaze was so often fixed. Their exit, however, would not take them near Beale's prison. A few paces along the corridor was another passage leading to the yard above, and it was by this way that Hilda Glaum had sped to the doctor's room. Presently all were gone save one industrious worker, who sat peering through the eye-piece of his microscope, immovable. "That's our friend Bridgers," said Milsom, "he's all lit up with the alkaloid of _Enythroxylon Coca_---- Well, Bridgers, nearly finished?" "Huh!" grunted the man without turning. Milsom shrugged his shoulders. "We must let him finish what he's doing. He is quite oblivious to the presence of anybody when he has these fits of industry. By the way, the passing of our dear enemy"--he jerked his head to the passage door--"will make no change in your plans?" "How?" "You have no great anxiety to marry the widow?" "None," said the doctor. "And she isn't a widow yet." It was not Milsom who spoke, but the man at the bench, the industrious worker whose eye was still at the microscope. "Keep your comments to yourself," said van Heerden angrily, "finish your work and get out." "I've finished." The worker rose slowly and loosening the tapes of his mask pulled it off. "My name is Beale," he said calmly, "I think we've met before. Don't move, Milsom, unless you want to save living-expenses--I'm a fairly quick shot when I'm annoyed." Stanford Beale pushed back the microscope and seated himself on the edge of the bench. "You addressed me as Bridgers," he said, "you will find Mr. Bridgers in a room behind that stack of boxes. The fact is he surprised me spying and was all for shooting me up, but I induced him to come into my private office, so to speak, and the rest was easy--he dopes, doesn't he? He hadn't the strength of a rat. However, that is all beside the point; Dr. van Heerden, what have you to say against my arresting you out of hand on a conspiracy charge?" Van Heerden smiled contemptuously. "There are many things I can say," he said. "In the first place, you have no authority to arrest anybody. You're not a police officer but only an American amateur."