Max Brand 
Out of the Dark [EPUB ebook] 

When he recovered his senses, it would be difficult to shoot effectively in the dark, for this was not the gloom of night—it was an absolute void, black, thick, impenetrable. She could not make out her hand at the slightest distance from her eyes. He might even attack her from behind and knock the revolver from her hand before she could shoot. Sooner or later the man must die. Even if she did not kill him it would be accomplished by the command of the prince at the end of the three days.