"THEY'RE TO MEET AT ROSAMOND'S POND" A masquerade was in full swing at a mansion in Leicester Square.

The air of the ball-room was hot and stuffy.

Ventilation was a thing of little account.

The light, albeit there were a hundred candles or so in the sconces, on the panelled walls, and in the chandelier hanging from the decorated ceiling, and despite the assiduous snuffing by the servants, was dim.

The subdued illumination was not without its advantage.