It is 1855, and engineer William May has returned home to London and his beloved wife from the horrors of the Crimean War. When he secures a job transforming the city's sewer system, he believes it will prove his salvation, as, in the subterranean world beneath the city, he begins to lay his ghosts to rest. But when the peace of the tunnels is shattered by a violent murder William loses his tenuous hold on his sanity. Implicated in the crime, plagued by nightmares and visions, he is no longer sure: Could he truly have committed it? Long Arm Tom, a tosher, is William's only hope of salvation.