London in the summer of 1849. With a deadly cholera epidemic threatening, young engineer Joshua Jeavons is convinced it is his mission to save the capital and reform its festering sewers. Meanwhile in his dometsic life he is troubled by the baffling coldness shown towards him by his beautiful bride, Isobella. As he struggles to win her round, he works feverishly on a revolutionary drainage plan. This is his dream, his dazzling vision of the future: a London free of effluent. Then a sudden and mystifying disappearance throws his whole life upside-down. He is forced to embark on a harrowing search, which plucks him from his respectable life and throws him into a London previously unknown to him. A netherworld of slum-dwellers, pickpockets and scavengers of the sewers. He will find it is this very world that holds unexpected answers to the mysteries that surround him.