I was standing at the window of Poirot's rooms looking out idly on the street below."That's queer," I ejaculated suddenly beneath my breath."What is, mon ami?" asked Poirot placidly, from the depths of his comfortable chair."Deduce, Poirot, from the following facts! Here is a young lady, richly dressed--fashionable hat, magnificent furs. She is coming along slowly, looking up at the houses as she goes. Unknown to her, she is being shadowed by three men and a middle-aged woman. They have just been joined by an errand boy who points after the girl, gesticulating as he does so. What drama is this being played? Is the girl a crook, and are the shadowers detectives preparing to arrest her? Or are they the scoundrels, and are they plotting to attack an innocent victim? What does the great detective say?"