Behind the Bronze Door by William Le Queux

Though several weeks had passed, no trace had been discovered of Mrs. Mervyn-Robertson's missing property. For reasons of her own she had prevented any mention of the robbery being made in the newspapers, and apparently even the Metropolitan Secret Agency had this time failed to make good.

Preparations were in progress for the great ball to be given at the Albert Hall by Aloysius Stapleton and his friend, young La Planta, and as Jessica still said she preferred not to act as hostess on that occasion, Stapleton had succeeded in enlisting the services of a well-known peeress who, helped by friends of her own, would receive his guests on the eventful night.