The Opal Serpent by Fergus Hume — Read

Hurd's sister was a clever young woman who in her time had played many parts. She began her career along with Hurd as a private detective, but when her brother joined the official service, Miss Hurd thought she would better her position by appearing on the stage, and, therefore, took the rather queer name of Aurora Qian. In her detective capacity she had often disguised herself when employed in obtaining evidence, and was remarkably talented in changing her face and figure. This art she used with great success in her new profession, and speedily made her mark as an impersonator of various characters out of novels. As Becky Sharp, as Little Dorrit, she was said to be inimitable, and after playing under several managements, she started, in the phrase of the profession, "a show of her own," and rapidly made money.

But her great faults amongst others were vanity and extravagance, so she was always in need of money, and when chance offered, through her brother, to make any, she was not averse to returning to the spy business. Thus it came about that she watched Mr. Grexon Hay for many a long day and night, and he never suspected the pretty, fluffy, kittenish Miss Qian was in reality an emissary of the law. Consequently, when Aurora asked him to a card-party at her rooms, Hay accepted readily enough, although he was not in need of money at the time.