The World's Desire by H. Rider Haggard

When Meriamun the Queen had watched the chariot of the Wanderer till it was lost in the dust of the desert, she passed down from the Palace roof to the solitude of her chamber.

Here she sat in her chamber till the darkness gathered, as the evil thoughts gathered in her heart, that was rent with love of him whom she had won but to lose. Things had gone ill with her, to little purpose she had sinned after such a fashion as may not be forgiven. Yet there was hope. He had sworn that he would wed her when Pharaoh was dead, and when Argive Helen had followed Pharaoh to the Shades. Should she shrink then from the deed of blood? Nay, from evil to evil she would go. She laid her hand upon the double-headed snake that wound her about, and spake into the gloom: