Most had sought shelter in the safe houses opening up in the quiet residential streets off Eastern Avenue and the ones left pounding the pavements were grouping together in twos and threes for some sort of protection. When one was picked up and driven off, her friend would ostentatiously write down the number in a notebook. The clients objected and there’d been a fracas or two resulting in even less activity on the street.

The regulars were not in evidence today. Warned off? Or stunned by the latest murder-the fourth of what was beginning to look sickeningly like a series. A corpse had been dragged out of a ditch to the south of the city, yesterday. Strangled, like the others.

They were beginning to call him the Clock Killer. Some clever dick brought in from the Metropolitan Police had plotted the dumping grounds, or the “deposition spots” as they called them these days, and come up with the theory that the man responsible was working his way around what would look like a clock face with Cambridge at the centre. The first girl had been killed and left in the Fens to the north at the number twelve on the dial. The second had been found in a country lane at ten past, the third south of Newmarket at twenty past, and this latest, due south on a golf course by the Gog-Magog hills. And all equidistant from the red-light area where they’d been picked up. Ten miles.

The brainiac from the Met had treated the media to a learned explanation of the compulsion that led to a villain choosing his spots with such (literal) clockwork precision. The watcher gave a thin smile. He knew better. These days every Tom, Dick, and Harry watched CSI programmes. Profiling, DNA analysis, trace evaluation… there were no more professional secrets. But the police went on assuming their man was an out-of-control noddy. The truth was, he was probably well clued-up about crime-location diagrams, comfort zones, crime-commission intervals, and all the rest of the semi-scientific garbage. The watcher knew exactly what the perpetrator was up to. By sticking to a prearranged pattern, the killer was sidestepping any attempt at analysis and concealing his base. He needn’t be the local man they had projected. He could be any London man with a map. It was as simple as that.