It was a still, balmy night in late October. The scent of burned autumn leaves hung in the air, and a hazy moon, showing just over the housetops, deepened the shadows on the streets.        Policeman Murphy stopped far a moment, as was his custom, at the corner of Lawrence Avenue and Sheridan Road. He knew that it was about two o'clock in the morning as that was the hour at which he usually reached this point. He glanced sharply up and down Sheridan Road, which at that moment seemed to be completely deserted save for the distant red tail-light of a belated taxi, the whir of whose engine came to him quite distinctly on the quiet night air.        JUST THEN POLICEMAN MURPHY HEARD A SHOT!        Instantly his body quickened with an awakened alertness, and he glanced east and west along the lonely stretch of Lawrence Avenue. He saw nothing, and concluded that the sound he had heard must have come from one of the many apartment buildings which surrounded him.        Murphy pondered for a moment. Was it a burglary, a domestic row, or perhaps a murder? The position of the shot was hard to locate, for it had been but the sound of a moment on the still night. Murphy, however, decided to take a chance, and started stealthily north on Sheridan Road, keeping within the shadow that clung to the buildings.