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282 Of the household there remained only Rannie and Gene, Peters, the cook, and the housemaid. Could it be that he had taken the servants too much for granted, and that among them the guilty person might be found?

Miss Meade did not return; and for the better part of an hour he sat there deep in thought, when all at once the bell rang. Recognizing Blake's silhouette through the frosted glass, he opened the door himself and ushered the operative quickly into the library.

"What did Villard say?" he demanded without preamble. "You had that sample doped out right, Sergeant" Blake grinned. "Villard told me to tell you that he used the Marsh test, and I watched him; I know a little about chemistry myself. He treated that stuff you gave me in the bottle with dilute sulphuric acid and metallic zinc in the gas generator and when the arsine formed he passed it through a glass tube and heated it. The metallic arsenic showed up all right and formed a mirror near the open end of the tube. There wasn't the chance of a mistake."

"Very good, Blake. Go and get your lunch and then relieve Shaw. I'll give you further instructions later."

He let the operative out quietly and started to ascend to the second floor, meaning to summon the doctor for a moment from the sickroom and acquaint him with what he had just learned, but paused. Someone was going up the second flight of stairs to the third floor; and a certain stealthy, cat-like quality in the creeping footsteps made him halt and listen. Could it be Peters, and if so, what was he doing up there when he should have been making his preparations for lunch? Whoever it was, the objective was evidently the servants'