The Lady in Blue by Fred M. White

Clutton crept along under the shelter of the counter. He knew perfectly well what had brought Blanche Trevenner here; indeed, he could pretty well imagine the conversation between her and Magavitch, but, seeing that he was by good fortune on the spot, he had no intention of letting this opportunity slip. For the present, at all events, the Princess would have to wait. It might be just possible to communicate with her by means of a sort of Morse code, which they had found useful on more than one occasion, and this could be conveyed by a series of taps on the floor. In the silence of the place Clutton could hear the scratching of mice and rats, and a queer, thumping noise one of the larger rodents was making, evidently in conveying some food from one place to another. In these circumstances it was possible to use the code without arousing any suspicion on Magavitch's part. Clutton judged that he must be very nearly over the cellar, and therefore his signal should be easily heard.

He tapped away steadily for a few seconds, and then stopped. His strained ears caught the sound of a chair being dragged over the floor below, so he knew that he had been understood. There was nothing for it now but to get as near the glass tank as possible and listen to what was going on inside.