The Safety Pin by J.S. Fletcher

Simmons' naturally acute brain, sharpened by his legal training, was busy enough as he sped towards home. That he had made a discovery he had no manner of doubt. Certain facts were obvious: he began to classify and label them. The man who disappeared so mysteriously from Normansholt was named James Arradeane, and he was a civil engineer by profession. The man found murdered at Southernstowe was named James Deane; and, according to Miss Pretty's statement, he, too, was a civil engineer. The Mrs.

Arradeane of Normansholt had a brother who lived with her and was a loafer: Mrs. Champernowne of Southernstowe also had a brother who lived with her and was a loafer--and looked as if he had never been anything else. As far as Simmons could reckon things up from the story given him by his new friend Swilford Swale, the Mr. and Mrs. Arradeane of Normansholt would now be about the apparent age of Mr. Deane, now deceased, and Mrs. Champernowne, still living. Was James Deane the same person as James Arradeane? Was Mrs. Champernowne Mrs. Arradeane? Simmons was disposed to answer both questions in the affirmative.