Number 70, Berlin by William Le Queux

Just before eleven o'clock that night Jack Sainsbury stopped at a large, rather severe house half-way up Wimpole Street -- a house the door of which could be seen in the daytime to be painted a royal blue, thus distinguishing it from its rather dingy green-painted neighbours.

In response to his ring at the visitors' bell, a tall, middle-aged, round-faced manservant opened the door.