It is 1855, and engineer William May has returned home to his beloved wife from the battlefields of the Crimea. He secures a job transforming London's sewer system and begins to lay his ghosts to rest. Above ground, his work is increasingly compromised by corruption, and cholera epidemics threaten the city.

But it is only when the peace of the tunnels is shattered by murder that William loses his tenuous hold on sanity. Implicated in the crime, plagued by visions and nightmares, even he is not sure of his innocence. Long Arm Tom, who scavenges for valuables in the subterranean world of the sewers and cares for nothing and no one but his dog, Lady, is William's only hope of salvation. Will he bring the truth to light?