Cain his brother

"Genevieve Stonefield's husband Angus has been missing for three days when she visits William Monk, a former police inspector turned private investigator. She is convinced Angus is dead, murdered by his twin brother Caleb. While her husband has long been a respected businessman, Caleb is a shadowy, dangerous figure living in the slums that border the Thames in Limehouse; the relationship between them, Monk is told, has often been violent, and Genevieve fears the worst. Monk is not ready to assume a murder has taken place, let alone pinpoint a killer, through he quickly confirms that Angus has indeed vanished. But why did Caleb's woman Selina visit Angus's office the morning he disappeared? And why is Caleb so different from his impeccably behaved brother? Without the authority or facilities of the police force behind him, Monk is thrown back on his own resources and the help of his friends, including his patroness Lady Callandra Daviot and nurse Hester Latterly, to bring one of the most bizarre and baffling cases he has ever encoutered to its thrilling conclusion." -- back cover.