“For the same reason that I pretended to change the bottle. For the benefit of the maid whom we saw just now in the bedroom.”
“And why for the benefit of the maid?”
“Because I found out this morning that she is in the pay of Grist. That discovery accounts for my nervousness to-night about Adelaide. By this time the maid has probably told Mr. Grist what has taken place, and, and—I shall rely on your help if anything should happen, doctor. Surely, surely, you believe me?”
“I regret to say, madam,” I answered, “that I find myself unable to believe you at present. But there is a simple way of giving credence to your story. You state that you did not exchange the bottles. This liquid, then, is the medicine prescribed by me, and it is harmless. Oblige me by drinking it.”
And I held the glass towards her.
She took it.
“Fool!” I said to myself, as soon as her fingers had grasped it. “She will drop it on the floor, and an invaluable piece of evidence will be destroyed.”
But she did not drop it on the floor. She drank it at one gulp, and looked me in the eyes, and murmured, “Now do you believe me?”
“Yes,” I said. And I did.
At the same moment her face changed colour, and she sank to the ground. “What have I drunk?” she moaned. The glass rolled on the carpet, unbroken.