The Chestermarke Instinct by J.S. Fletcher

Neale, who had never seen a real, live detective in the flesh, but who cherished something of a passion for reading sensational fiction and the reports of criminal cases in the weekly newspapers, looked at the man from New Scotland Yard with a feeling of surprise. He knew Detective-Sergeant Starmidge well enough by name and reputation. He was the man who had unravelled the mysteries of the Primrose Hill murder -- a particularly exciting and underground affair. It was he who had been intimately associated with the bringing to justice of the Camden Town Gang -- a group of daring and successful criminals which had baffled the London police for two years. Neale had read all about Starmidge's activities in both cases, and of the hairbreadth escape he had gone through in connection with the second. And he had formed an idea of him -- which he now saw to be a totally erroneous one. For Starmidge did not look at all like a detective -- in Neale's opinion. Instead of being elderly, and sinister, and close of eye and mouth, he was a somewhat shy-looking, open-faced, fresh-coloured young man, still under thirty, modest of demeanour, given to smiling, who might from his general appearance have been, say, a professional cricketer, or a young commercial traveller, or anything but an expert criminal catcher.

"Only just got here, and a bit tired, miss," continued Polke, waving his hand again at the detective. "So I'm just giving him a refresher to liven his brains up. He'll want 'em -- before we've done."