The Great God Gold by William Le Queux

Laura, the parlour-maid, had been let in at the area-door by the cook, to whom she had made her excuses for the lateness of the hour, and had crept up to her room, fully satisfied at having assisted her good-looking lover. She was, of course, in utter ignorance that "Mr Miller" was the person to whom Miss Gwen's mysterious absence from home had been due. Otherwise she certainly would not have fallen into the trap.

Meanwhile, in the study, with the typed folios of the cipher before him, the old Professor sat making certain explanations to his daughter and answering her eager questions.