The Safety Pin by J.S. Fletcher

Of the four men in that room, the quickest to grasp the situation was Simmons.

He saw at once what had happened during his absence. Palsford had not only gone to Shelmore about Sir Reville Childerstone's business, but had told him all about the Arradeane mystery at Normansholt, and had probably seen Mrs. Champernowne and recognised her as the Mrs. Arradeane he had known in his own town. And Shelmore had taken him to the police--and here was Mellapont with both of them, obviously wanting Miss Pretty. Why? Clearly, he must act, and act quickly, if he wanted to be first.