Betty put out a hand and laid it on Ann's shoulder and held her so for a moment, savouring her vengeance.
"Whose face was it bending so close down over yours in the darkness?" she asked in a soft and dreadful voice. "Whose face, Ann? Guess!" She shook her swaying prisoner with a gentleness as dreadful as her quiet voice. "You talk too much. Your tongue's dangerous, Ann. You are too curious, Ann! What were you doing in the treasure-room yesterday evening with your watch in your hand? Eh? Can't you answer, you pretty fool?" Then Betty's voice changed. It remained low and quiet, but hatred crept into it, a deep, whole-hearted hatred.
"You have been interfering with me too, haven't you, Ann? Oh, we both understand very well!" And Hanaud's hand tightened upon Frobisher's shoulder. Here was the real key and explanation of Betty's hatred. Ann Upcott knew too much, was getting to know more, might at any moment light upon the whole truth. Yes! Ann Upcott's disappearance would look like a panic-stricken flight, would have the effect of a confession—no doubt! But above all these considerations, paramount in Betty Harlowe's mind was the resolve at once to punish and rid herself of a rival.
"All this week, you have been thrusting yourself in my way!" she said. "And here's your reward for it, Ann. Yes. I had you bound hand and foot and brought here. The water-lily!" She looked her victim over as she stood in her delicate bright frock, her white silk stockings and satin slippers, swaying in terror. "Fifteen minutes, Ann! That fool of a detective was right! Fifteen minutes! That's all the time the arrow-poison takes!"
Ann's eyes opened wide. The blood rushed into her white face and ebbed, leaving it whiter than it was before.
"Arrow-poison!" she cried. "Betty! It was you, then! Oh!" she would have fallen forward, but Betty Harlowe pushed her shoulder gently and she fell back upon the divan. That Betty had been guilty of that last infamy—the murder of her benefactress—not until this moment had Ann Upcott for one moment suspected. It was clear to her, too, that there was not the slightest hope for her. She burst suddenly into a storm of tears.
Betty Harlowe sat down on the divan beside her and watched her closely and curiously with a devilish enjoyment. The sound of the girl's sobbing was music in her ears. She would not let it flag.
"You shall lie here in the dark all night, Ann, and alone," she said in a low voice, bending over her, "To-morrow Espinosa will put you under one of the stone flags in the kitchen. But to-night you shall lie just as you are. Come!"
She bent over Ann Upcott, gathering the flesh of her arm with one hand and advancing the needle with the other; and a piercing scream burst from Francine Rollard.
"Look!" she cried, and she pointed to the door. It was open and Hanaud stood upon the threshold.