River of Darkness by Rennie Airth
As rural England slowly emerges from the sorrow of World War I, a particularly vicious attack on a household in a small Surrey village leaves five butchered bodies and no explanation for the killings. Sent by Scotland Yard to investigate is Inspector John Madden, a man still recovering from his own war experience and from the deaths of his wife and child. The local police dismiss the slaughter as a botched robbery, but Madden detects the signs of a madman at work. With the help of beautiful Dr. Helen Blackwell, who introduces him to the new science of criminal psychology, Madden sets out to capture the killer, even as the murderer sets his sights on his next innocent victims.As darkly stylish as the best P. D. James, rippled with tension and resonant with historical atmosphere, River of Darkness marks the debut of a powerful new voice in suspense writing.