1864 and, once again, Inspector William Monk, now of the Thames River Police, must face a dangerous foe. After a game of cat and mouse, Monk has finally captured Jericho Philipps, main suspect in the brutal slaying of mudlark Water 'Fig' Figgis. In doing so he believes that he has taken the first step in bringing to justice the man responsible for running an evil child prostitution ring and avenged the memory of Durban, his old commander, who was convinced of Philipps' guilt. When Philipps comes to trial however all does not run smoothly. Oliver Rathbone, Monk's friend, is hired anonymously to represent Philipps and he immediately casts doubts over the police case. The result is that Philipps is swiftly freed. Monk, determined to prove Philipps' guilt, begins the investigation again. But as he ventures deeper into London's murky underworld, he realises that Durban may have had another reason for pursuing Philipps and, even more worryingly, that Philipps' depraved tastes reach further into civilised society than anyone could have ever imagined!