Genvieve Stonefields husband Angus is missing when she seeks William Monks help to find him. She is convinced that he has been murdered by his twin brother Caleb a shadowy figure who lives in the slums bordering the Thames & has always hated his respectable businessman brother. Although worried about Hester Latterlys health as she nurses victims of a typhoid outbreak in Limehouse & threatened by a personal scandal Monk is determined to bring one of the most bizarre cases he has ever encountered to its conclusion.