Grim Vengeance — J.J. Connington

From the dustjacket of the first edition: “Two murders at night, both the victims foreigners; and when Sir Clinton Driffield, visiting his sister, is forced to suspect the South American whom his niece has just married, he finds himself faced with a problem in morals and psychology. Finally, a third murder takes place, this one in the house of Sir Clinton's sister, and in broad daylight. Suspicion naturally falls on a young man who is found standing beside the body with a pistol in his hand; but Sir Clinton clears him, only to find that his own niece is the next suspect. In the course of the narrative, all the evidence known to the police (and even a little more) is supplied to the reader as it comes to light; but it is safe to say that the final development of the plot will be wholly unexpected. To quote the  London Times:  ‘Mr. Connington has established his name in the front rank of detective story writers, and this novel is one of his finest achievements.'”